ELECTRICITY 
ITS  HISTORY  AND  DEVELOPMENT 


The  Leyden  experiment.     The  first  storage  of  electricity 


ELECTRICITY 

ITS  HISTORY 
AND  DEVELOPMENT 


BY 

WILLIAM  A.  DURGIN 


WITH    ILLUSTRATIONS 


CHICAGO 
A.  C.  McCLURG  &  CO. 

1912 


Copyright 
A.  C.  McCLURG  &  CO. 

1912 


Published  October,  1912 


F.  HALL  PRINTING  COMPANY.  CHICA3O 


To  My  Wife 
LAURA  KELLOGG  WEAVER  DURGIN 


255786 


FOREWORD 

book  is  intended  for  the  man  who  desires 
-•-  a  fair  understanding  of  present-day  elec- 
tricity, but  who  finds  the  statements  of  the  text- 
books and  manuals  more  detailed  than  he  needs  and 
a  bit  too  dry  to  hold  his  interest.  By  considering 
the  main  events  in  the  development  of  electrical 
applications  it  seemed  possible  to  preserve  some  of 
the  romance  of  the  work  of  the  pioneers,  past  and 
present,  and  at  the  same  time  to  give  clear  con- 
ceptions of  the  fundamentals.  This  has  been  at- 
tempted in  the  following  pages;  and  if  the  work 
serves  to  lighten  the  mystery  of  electricity  for  a 
few,  or  to  show  the  charm  and  adventure  which 
still  await  those  who  choose  electrical  work  as  their 
vocation,  it  will,  perhaps,  have  justified  publication. 

W.  A.  D. 


CONTENTS 

CHAPTER  PAGE 

I     THE  OCCASIONAL  DISCOVERIES  OF 

TWENTY-THREE  CENTURIES       .     .  13 

II     THE   AMERICAN   PROMETHEUS     .     .  26 

III  THE  CONVULSED  FROG-LEG  AND 

WHAT  CAME  OF  IT 36 

IV  "THE  ELECTRIC  CONFLICT"  ...  47 
V     AN  ANCHOR  RING  AND  WHAT  IT 

HELD 58 

VI     THE  UNITS 67 

VII     THE  SYMPATHETIC  NEEDLE    ...  77 

VIII     FROM  TELEGRAPH  TO  TELEPHONE   .  87 

IX     THE  ELECTRIC  ARCH 98 

X     THE  HEAT  OF  NIAGARA     .     .     .     .  108 

XI     THE   BAMBOO   LIGHT     .     .     ,.     .     .  118 

XII     THE  ELECTRICAL  REVOLUTION     .     .  130 

XIII     A  BLACKSMITH  AND  His  DREAM   .     .  141 

XIV     THE  MYSTERY  OF  THE  IRON  Box     .  151 

XV     THE  SPIRIT  OF  ELECTRICITY  .     .     .  161 


ILLUSTRATIONS 

PAGE 
The  Leyden  experiment.  The  first  storage  of 

electricity Frontispiece 

von  Guericke's  electrical  machine  and  sulphur  globe  .  20 

Leyden  jars  connected  in  series 30 

Leyden  jars  connected  in  parallel 30 

An  early  form  of  trough  battery  containing  twenty- 
seven  '  '  cells ' '  in  series 30 

Volta's  pile,  the  first  generator  of  a  continuous  elec- 
trical current 38 

The  ' '  crown  of  cups ; '  devised  by  Volta 38 

Oersted's  original  experiment — the  magnetic  action  of 

' '  the  electric  conflict " 48 

The  multiplication  of  the  magnetic  effect  of  a  current 

by  a  winding  "turn" 48 

Ampere's  table  and  coils  used  in  his  electro -magnetic 

discoveries 48 

Lines  of  magnetic  force  from  two  permanent  magnets 

shown  by  iron  filings 49 

Iron  filing  diagram  of  magnetic  lines 49 

Faraday's  anchor  ring  with  which  he  discovered  the 

induction  of  electric  current 58 

The  first  electric  generator  producing  direct  currents  .  58 
Fleming 's  l '  right  hand  rule ' '  showing  the  relation  of 

the  direction  of  the  e.  m.  f 62 

Faraday's  rectangle  for  generating  electric  current 

from  the  earth's  magnetic  field     ....        ...  62 

Standard  I-ohm  resistance  coil,  arranged  for  immersion 

in  oil  bath  to  secure  constant  temperature  ....  72 

Arrangement  of  iron  filings  in  plane 72 

Standard  Weston  cell,  adopted  as  legal  standard  of 

e.  m.  f. 73 

Vibrator  used  in  induction  coils  and  in  electric  bells  .  73 

Siemen's  generator  with  shuttle  armature  ....  73 

Cooke  and  Wheatstone  's  original  five-needle  telegraph  .  82 

The  first  Morse  telegraph 82 

The  simple  telegraph  circuit  86 

Bell's  vibrating  multiplex  telegraph  and  its  effect  on 

line  current    .  ....  .86 


Illustrations 

PAGE 

Bell  telephone  as  described  in  the  original  patent     .     .  87 
Bell's  magneto  electric  telephone — the  first  entirely  suc- 
cessful telephone  instrument 87 

The  Hughes  microphone 94 

An  early  form  of  Edison  carbon  transmitter     ....  94 
Edison's  application  of  the  induction  coil  to  long  dis- 
tance telephony 94 

Mechanism  of  the  first  successful  arc  lamp 106 

The  first  electric  heating  device — spark  used  to  ignite 

ether 106 

Lenz's    current    calorimeter       116 

The  arc  type  of  electric  furnace 116 

The  first  commercial  application  of  electric  heat — Cowles 

resistance  furnace       116 

Starr's  lamp 120 

De  la  Kue's  platinum  light 120 

The   bamboo   filament   Edison   lamp 120 

Assembling  bulb  and  filament  for  welding 121 

Metallized  carbon  lamp 121 

Tungsten  "wire  type"  lamp 128 

Faraday  7s  first  device  for  showing,  the  electrical  revolu- 
tion          132 

Lines  of  force  about  a  north  magnetic  pole     ....  132 

Fleming's    "left   hand   rule" 133 

Rearrangement  of  Faraday's  device 133 

Barlow's  wheel 133 

Further  development  of  Faraday 's  device  showing  evolu- 
tion of  modern  motor  armature 136 

Six  pole  modern  motor 136 

Edison  experimental  railway  at  Menlo  Park     ....  144 

Original  Edison  dynamo 145 

Modern  G.  E.  "split  frame"  40  H.  P.  railway  motor     .  145 

G.  E.  type  K-36-F  controller 146 

Simple  alternating  current  generator 154 

Alternating    pressure    wave    form    of    Commonwealth 

Edison  Company's  25  cycle   system 154 

Simple  transformer  developed  from  Faraday's  anchor 

ring        155 

Elementary  A.  C.  circuit  showing  two  transformers     .  155 

External  appearance  of  modern  lighting  transformer     .  158 


ELECTRICITY 

ITS  HISTORY 
AND  DEVELOPMENT 

I 

THE  OCCASIONAL  DISCOVERIES  OF  TWENTY-THREE 
CENTURIES 

T^LECTRICITY!  What  is  it?  Who  discovered 
-•— '  it?  What  ideas  are  hidden  in  this  jargon  of 
"volts,"  "amperes,"  and  "kilowatts,"  which  the 
electrical  man  uses  in  his  kind  efforts  to  make  all 
clear?  Surely  there  must  be  some  simple  way  of 
representing  the  energy  which  now  supplies  our  best 
light,  our  best  power,  and  our  best  transportation. 
The  fundamentals  are  but  the  result  of  slow  ele- 
mentary evolution ;  and  by  reviewing  the  main  steps 
of  this  evolution  we  should  find  it  easy  to  get  a  few 
conceptions  which  will  make  the  electric  generator 
as  familiar  as  the  steam  boiler,  the  electric  motor 
as  the  steam  engine,  the  tungsten  lamp  as  the  gas 
flame;  which,  in  short,  will  make  commonplace  of 
the  mystery. 

585  B.  c.  is  usually  taken  as  the  birthdate  of 
[13] 


Electricity:   Its  History  and  Development 

electricity,  for  it  represents  the  period  of  Thales, 
who  is  reported  by  Aristotle  to  have  said,  "  The 
stone  has  a  soul  since  it  moves  iron." 

Something  over  twenty-five  hundred  years  ago, 
then,  it  had  been  discovered  that  certain  pieces  of  a 
particular  iron  ore,  the  variety  now  called  magnetite, 
possessed  the  power  of  attracting  other  similar 
pieces  and  of  moving  small  articles  of  iron,  and  it 
was  this  commonly  known  phenomenon  which 
Thales  first  recorded  in  his  fantastic  theory.  The 
best  specimens  of  these  stones  were  obtained  in  the 
City  of  Magnesia  and  before  many  centuries  the 
name  "  magnets  "  was  coined.  The  first  word  of 
our  technical  vocabulary  and  Thales'  scientific  fame 
are  thus  both  connected  with  magnetism,  the  science 
of  the  properties  of  magnets ;  and  although  we  shall 
find  these  magnetic  actions  to  be  very  closely  inter- 
mingled with  most  present  applications  of  electric- 
ity, we  must  admit  that  such  efforts  are  not  strictly 
electric.  This  latter  term  is  reserved  for  phenomena 
growing  out  of  another  observation  of  the  ancients ; 
that  when  the  mineralized  resin,  amber,  was  rubbed,  it 
exhibited  an  attraction  for  light  materials;  but  as 
this  effect  was  early  classed  with  that  of  the  mag- 
net it  has  been  assumed,  with  somewhat  weak  logic, 
that  Thales  knew  of  it,  and  that  he  may  be  fully 
accredited,  therefore,  as  the  earliest  electrical  dis- 
coverer. 

[14] 


Discoveries  of  Twenty-three  Centuries 

The  beautiful  golden  amber,  named  electron  by 
the  Greeks  for  its  suggestion  of  sunlight,  was  used 
for  jewelry  from  the  earliest  times,  and  the  attract- 
ive power  of  hair  ornaments  or  of  the  spindles 
made  for  the  wealthier  women's  spinning  must  have 
been  soon  noticed.  But  although  the  amber  attrac- 
tion was  thus  probably  known  long  before  that  of 
the  magnet,  no  definite  description  occurs  in  an- 
cient writings  until  about  300  B.  c.,  when  Theo- 
phrastus  notes  that,  "  Amber  is  a  stone.  It  is  dug 
out  of  the  earth  in  Liguria  and  has  a  power  of  at- 
traction. It  is  said  to  attract  not  only  straws  and 
small  pieces  of  sticks,  but  even  copper  and  iron,  if 
they  are  beaten  into  thin  pieces."  In  this  quota- 
tion and  that  from  Aristotle  are  presented  a  com- 
plete summary  of  recorded  electrical  and  magnetic 
knowledge  for  over  fifteen  hundred  years,  with  the 
single  exception  that  some  time  before  100  A.  D. 
it  had  been  observed,  as  Plutarch  writes,  that  "iron 
drawn  by  stone  often  follows  it,  but  often  also  is 
turned  and  driven  away  in  the  opposite  direc- 
tion." 

About  the  middle  of  the  twelfth  century,  a  prac- 
tical use  for  the  magnet's  properties  was  found,  in 
the  compass.  This  device,  first  described  in  1180 
by  Alexander  Neckham,  an  English  monk,  is 
often  credited  to  the  Chinese,  but  was  probably  in- 
vented by  sailors  of  Northern  Europe.  It  implies 

[is] 


Electricity:   Its  History  and  Development 

a  knowledge  of  the  facts  that  (a)  when  a  natural 
magnet  —  or,  as  it  now  came  to  be  called,  a  "  lode- 
stone"  or  "leading  stone" — is  suspended  and 
free  to  turn  about  a  vertical  axis  it  will  always  take 
a  position  such  that  the  same  definite  portion  is 
toward  the  north,  and  (b)  that  by  rubbing  a  piece 
of  iron  with  the  lodestone  the  attractive  and  direct- 
ive properties  of  the  stone  may  be  temporarily 
imparted  to  the  iron. 

The  first  compasses  consisted  of  needles  of  iron 
thrust  through  pieces  of  wood  and  floated  in  ves- 
sels of  water.  The  needles  were  only  used  in  cases 
when  the  pole  star  could  not  be  seen,  and  had  to 
be  rubbed  with  the  lodestone  or  magnetized  each 
time.  A  very  crude  instrument,  this,  but  quite  suffi- 
cient to  lead  to  the  discovery  of  a  new  continent, 
quite  sufficient  to  put  the  magnet  and  amber  at- 
tractions first  among  the  phenomena  interesting 
Roger  Bacon  and  his  contemporaries.  Small  dis- 
coveries were  made  by  many  philosophers,  and  when 
in  Elizabeth's  reign  her  physician,  Dr.  William 
Gilbert,  took  up  the  subject  as  an  avocation  for  his 
leisure,  he  found  a  considerable  accumulation  of 
data,  true  and  false,  as  a  basis  for  the  researches 
which  have  gained  him  the  name  of  the  father  of 
electricity.  The  ends  of  the  suspended  magnet 
pointing  to  the  north  and  south  were  already  named 
the  poles,  and  it  had  been  found  that  the  north  pole 
[16] 


Discoveries  of  Twenty-three  Centuries 

of  one  magnet  attracted  the  south  pole  of  another, 
a  fact  which  Gilbert  verified,  although  he  misin- 
terpreted the  equally  true  relation  that  two  south 
poles  or  two  north  poles  repel  each  other. 

It  had  been  observed,  too,  that  the  magnetic  force 
was  manifested  at  a  considerable  distance  from  the 
lodestone.  Robert  Norman  had  conceived  the  idea 
that  the  magnet  was  surrounded  by  a  "sphere  of 
vertue,"  and  wrote :  "  I  am  of  the  opinion  that  if 
this  vertue  could  by  anie  means  be  made  visible  to 
the  eie  of  man,  it  would  be  found  in  sphericall  forme, 
extending  round  about  the  stone  in  great  compasse 
and  the  dead  bodie  of  the  stone  in  the  middle 
thereof."  As  in  most  cases,  Gilbert  improved  this 
theory,  imagining  the  sphere,  or,  as  he  called  it, 
"  orb  of  vertue,"  extending  to  remotest  space,  the 
magnetic  force  being  exercised  along  lines  which  he 
called  rays  of  magnetic  force.  Today  instead  of  the 
"  orb  of  vertue  "  we  speak  of  the  field  of  force  sur- 
rounding a  magnetic  pole ;  and  Gilbert's  "  rays  " 
are  now  called  lines  of  force,  but,  as  will  be  noted 
later  in  reviewing  Faraday's  discoveries,  the  present 
ideas  of  the  space  surrounding  a  magnetic  pole  are 
very  similar  to  Gilbert's  theory.  Norman's  discovery 
in  1576  that  in  England  a  needle  suspended  to  turn 
freely  about  a  horizontal  axis  pointed  down  toward 
the  north,  or  dipped,  cleared  another  path  for  Gil- 
bert, for  it  was  soon  found  that  the  dip  varied  with 

[IT] 


Electricity:   Its  History  and  Development 

location,  being  0°  at  the  equator  and  increasing 
toward  the  poles. 

From  this  dipping  and  the  attraction  of  unlike 
poles  Gilbert  evolved  the  theory  that  the  earth  itself 
was  a  magnet,  testing  his  conclusions  by  construct- 
ing a  small  globe  of  lodestone  toward  which  small 
needles  behaved  in  exactly  the  way  that  the  compass 
and  dipping  needle  acted  toward  the  earth.  He  saw 
at  once  that  the  magnetic  pole  of  the  earth  at  the 
north  geographical  pole  would  be  called  north,  and 
hence  the  pole  of  the  compass  pointing  north  ought 
to  be  called  south  and  not  north,  as  was  and  is  the 
universal  custom.  This  has  always  led  to  confusion 
which  can  be  avoided  only  by  taking  the  compass 
needle  as  the  standard,  and  agreeing  that  the  mag- 
netic pole  of  the  earth  which  lies  near  Peary's  goal 
is  south. 

Experimenting  with  a  dipping  needle  on  his  lode- 
stone  globe,  and  observing  that  the  dip  was  0°  at 
the  equator  and  increased  gradually  toward  the 
poles,  until  at  these  two  points  the  needle  became 
vertical  or  dipped  90°,  Gilbert  came  to  the  con- 
clusion that  a  dipping  needle  could  be  used  to  de- 
termine latitude.  Here,  unfortunately,  he  went 
astray,  for  although  the  dipping  needle  is  hori- 
zontal near  the  equator  and  does  become  vertical 
at  the  magnetic  poles  of  the  earth,  these  poles  do 
not  coincide  with  the  geographical  poles,  and  the 
[18] 


Discoveries  of  Twenty-three  Centuries 

unequal  distribution  of  the  earth's  magnetism  leads 
to  wide  deviations  from  the  uniform  variation  of 
dip  which  Gilbert  assumed.  The  error  was  soon 
discovered  in  the  attempt  to  use  the  dipping  needle 
in  navigation,  and  engendered  so  much  hostile  crit- 
icism as  to  retard  the  acceptance  of  the  truth  of 
the  earth's  magnetism. 

Beside  this  greatest  of  magnetic  discoveries  Gil- 
bert also  found  that  the  attraction  of  a  magnet  for 
iron  can  not  be  cut  off  by  interposing  any  substance 
except  an  iron  plate ;  that  the  attracted  iron  or  steel 
body  is  magnetized  before  it  touches  the  magnet  — 
or,  as  we  now  say,  magnetized  by  induction  —  hav- 
ing a  polarity  opposite  to  that  of  the  magnet,  so 
that  a  north  magnet  pole  induces  a  south  pole  in  the 
approaching  iron  and  these  unlike  poles  attract; 
that  the  magnetic  force  moves  from  one  end  of  an 
iron  rod  to  the  other,  so  that  magnetic  attraction  is 
manifested  at  the  distant  end  of  a  rod  in  contact 
with  a  magnet;  and  that  although  the  magnetic 
action  is  strong  only  at  the  poles,  the  force  per- 
meates every  part  of  the  mass,  for  when  the  stone 
or  steel  is  broken  into  particles,  no  matter  how 
small,  each  proves  to  be  a  magnet  with  new  poles. 
It  is  doubtful,  however,  whether  he  observed  that 
when  one  polarity  is  induced  at  the  near  end  of  a 
rod,  the  opposite  polarity  appears  at  the  far  end, 
or  that  the  induced  poles,  though  never  attaining 

[19] 


Electricity:   Its  History  and  Development 

the  strength  of  the  inducing  magnet,  grow  stronger 
as  the  iron  approaches  it. 

Turning  from  his  work  with  the  lodestone,  Gil- 
bert began  a  series  of  careful  experiments  upon  the 
amber  attractions.  He  was  rewarded  with  the  dis- 
covery that  not  only  amber,  but  a  large  class  of 
other  substances,  manifest  the  property.  From  this 
discovery  dates  the  recognition  of  electricity  as  a 
separate  science,  for  Gilbert  demonstrated  at  once 
that  there  was  nothing  in  common  between  this 
attraction  for  any  light  object  which  brisk  rubbing 
excited  in  more  than  half  of  the  substances  he  tried, 
and  the  natural  attraction  of  the  lodestone  for  iron 
only.  The  amber  attraction  was  evidently  a  much 
more  general  property,  and  for  those  bodies  which 
possess  it  he  invented  the  name  "  electrica, "  or 
electrics,  thus  supplying  the  root  for  the  word 
which  soon  came  into  use,  electricity. 

The  quickening  scientific  interest  of  Europe 
found  in  the  new  "  electrics  "  a  broad  field  for  ex- 
periment. Some  time  about  1650  Otto  von  Guer- 
icke,  burgomaster  of  Magdeburg,  bethought  him 
that  a  machine  might  be  constructed  to  do  the  brisk 
rubbing  with  less  labor.  He  built  a  ball  of  sul- 
phur on  a  shaft  which  could  be  readily  twirled  while 
the  palm  of  the  hand  was  applied  as  the  rubber  on 
the  surface  of  the  globe.  With  this  apparatus  for 
a  source  of  electricity  he  discovered  that  just  as 
[20] 


1 


•»* 

*"<u 

I 
o 


Discoveries  of  Twenty-three  Centuries 

magnetism  passes  from  one  end  of  an  iron  rod  to 
the  other,  so  the  electric  attraction  passes  along  a 
linen  thread  placed  in  contact  with  the  globe  and 
appears  at  the  distant  end;  that  is,  the  thread 
conducts  the  electricity,  or  is  a  conductor.  A  very 
poor  conductor  it  is,  transmitting  an  attraction 
hardly  sufficient  to  deflect  the  thread  toward  an  ap- 
proaching finger;  but  here,  in  the  burgomaster's 
workroom,  is  born  the  electrical  transmission  of  en- 
ergy. Some  fifty  years  later  Francis  Hawksbee 
substituted  a  glass  globe  for  the  ball  of  sulphur  and 
belted  the  shaft  to  a  large  wheel  with  crank 
attached,  so  that  high  speeds  of  revolution  could  be 
obtained.  When  this  glass  globe  was  exhausted  of 
air  and  rubbed,  a  beautiful  glow  light  filled  the 
sphere,  and  the  English  Royal  Society  meetings 
became  agitated  with  discussions  of  the  "  new  elec- 
tric light." 

But  the  attention  of  the  society  was  soon  taken 
by  the  discoveries  of  Stephen  Gray,  who  succeeded 
in  conducting  the  electric  attraction  nearly  1,000 
feet  over  threads  of  hemp,  supported  on  silk 
threads.  He  found,  however,  that  the  experiment 
failed  when  he  used  metal  wires  for  a  support ;  and 
thus  he  was  led  to  further  experiments,  which 
showed  that  while  linen,  hemp,  or  metal  would  con- 
duct electricity,  silk  would  not.  Evidently,  then, 
the  metal  supports  conducted  the  electricity  away 
[21] 


Electricity:   Its  History  and  Development 

from  the  hemp  thread  before  it  reached  the  distant 
end,  while  the  silk  supports  offered  no  conducting 
path.  Chas.  du  Fay,  a  Frenchman,  repeating 
Gray's  experiments  in  1733,  speaks  of  the  hemp 
threads  as  being  insulated,  when  supported  by  silk. 
From  this  we  have  our  present  use  of  the  term 
insulator,  as  meaning  any  substance  which  conducts 
electricity  so  poorly  that  for  practical  purposes  we 
may  consider  such  conduction  to  be  zero. 

With  this  conception  of  an  insulator  once  formu- 
lated, Du  Fay  proceeded  to  experiments  which 
quickly  showed  him  that  Gilbert's  "  non-electrics  " 
—  bodies  which  failed  to  become  electrified  when 
rubbed  —  were  simply  conductors,  and  that  when 
these  conducting  bodies  were  mounted  on  an  insu- 
lating base  or  handle,  friction  at  once  produced 
electrification.  In  Gilbert's  experiments  the  elec- 
trification or  charge  of  electricity  which  the  friction 
had  generated  on  his  non-electrics  had  been  con- 
ducted away  immediately  by  the  experimenter's 
body,  while  the  charge  stayed  on  the  insulators,  or 
electrics,  until  gradually  dissipated  by  moisture 
particles  in  the  air.  This  dissipating  effect  of  mois- 
ture follows  from  another  contribution  of  Du  Fay, 
for,  after  verifying  Von  Guericke's  observation  that 
a  feather  was  first  attracted  to  an  electrified  rod  and 
then  repelled,  he  came  to  the  conclusion  that  the 
feather  was  electrified  by  contact  with  the  rod  and 
[22] 


Discoveries  of  Twenty-three  Centuries 

that  electrified  bodies  repel  one  another.  Particles 
of  moisture,  thus,  are  attracted  to  a  charged  body, 
electrified  and  repelled,  each  particle  carrying  away 
a  tiny  part  of  the  total  quantity  of  electricity. 

No  sooner  was  this  theory  of  the  repulsion 
worked  out  than  Du  Fay  obtained  results  which  ap- 
parently disproved  it.  The  feather  or  bit  of  gold 
leaf,  after  touching  the  glass  rod,  was  repelled,  to 
be  sure,  but  it  was  attracted  by  a  piece  of  electrified 
resin!  He  soon  saw,  however,  that  all  the  effects 
could  be  explained  on  the  assumption  of  two  kinds 
of  electricity — -one  produced  by  rubbing  glass, 
which  therefore  he  called  vitreous;  the  other  by 
rubbing  resin,  and  hence  named  resinous.  Two 
bodies  electrified  with  the  same  kind  of  electricity, 
then,  repelled,  but  two  oppositely  electrified  bodies 
attracted  each  other.  This  explanation,  the  two- 
fluid  theory  of  electricity,  as  it  is  called,  has  long 
since  been  discarded  as  a  true  statement  of  physical 
facts,  but  it  is  still  of  use  in  affording  a  simple  con- 
ception of  the  phenomena. 

All  these  effects  depending  upon  the  influence  of 
rubbed  glass  rods  or  revolving  globes  were  neces- 
sarily feeble  because  of  the  small  size  of  the  electric 
machines.  Could  not  some  way  be  devised  of 
accumulating  or  storing  the  electricity  —  adding 
the  product  of  the  machine  little  by  little  until  a 
considerable  amount  was  obtained?  Thus  thought 
[23] 


Electricity:   Its  History  and  Development 

Von  Kleist,  Bishop  of  Pomerania,  in  1745.  Glass 
was  known  to  be  a  good  insulator  and  water  a  good 
conductor,  so,  partly  filling  a  glass  bottle  with  water 
and  arranging  a  nail  to  lead  from  the  machine  to 
the  water,  he  held  the  bottle  in  one  hand  and  worked 
his  machine  with  the  other.  After  some  minutes 
he  tried  to  disconnect  the  nail  and  was  greatly  ter- 
rified to  "  receive  a  shock  which  stuns  my  arms  and 
shoulders."  He  had  succeeded  —  the  electricity  had 
accumulated  far  beyond  his  expectations  —  and  the 
Leyden  jar  was  discovered.  The  discovery  was 
remade  independently  at  the  University  of  Leyden 
in  the  same  year;  whence  the  name  of  the  jar. 
Experiments  soon  showed  that  the  hand  outside  the 
glass  was  just  as  important  as  the  water  within, 
and  hand  and  water  were  replaced  with  tinfoil  coat- 
ings as  in  the  jars  now  used.  This  led  at  once  to 
the  discovery  that  the  outer  coating  must  be  con- 
nected to  the  rubber  of  the  machine  for  the  best 
action;  and  that  the  larger  the  jar  the  greater  was 
the  accumulation. 

Here  at  last  was  sufficient  electricity  to  produce 
a  real  stir  in  the  world.  Writing  in  1795,  Cavallo 
says: 

In  short  nothing  contributed  to  make  Electricity  the 
subject  of  the  public  attention  and  excite  a  general 
curiosity  until  the  capital  discovery  of  the  vast  accumu- 
lation of  its  power  in  what  is  commonly  called  the  Ley- 

[24] 


Discoveries  of  Twenty-three  Centuries 

den  phial,  which  was  accidentally  made  in  the  year  1745. 
Then,  and  not  till  then,  the  study  of  Electricity  became 
general,  surprised  every  beholder,  and  invited  to  the 
houses  of  electricians  a  greater  number  of  spectators 
than  were  ever  assembled  together  to  observe  any 
philosophical  experiments  whatsoever. 

What  some  of  these  experiments  were  and  what 
light  was  thrown  on  the  nature  of  this  new  mysteri- 
ous energy  we  must  now  consider. 


[25] 


II 

THE  AMERICAN  PROMETHEUS 

BENJAMIN  FRANKLIN,  printer,  in  Mr. 
Penn's  colony  in  America,  turned  for  amuse- 
ment, about  1746,  to  repeating  the  newly  published 
experiments  with  rubbed  glass  tubes  and  Le}rden 
phials.  With  true  beginner's  luck  he  at  once  made 
the  discovery  that  a  metal  point  held  near  an  elec- 
trified body  discharged  the  electrification  without 
the  passage  of  sparks.  When  the  experiment  was 
made  with  a  charged  cannon  ball  and  a  pin  in  the 
darkened  room,  a  glow  could  be  seen  at  the  pin 
point  but  no  sound  was  heard,  and  the  phenomenon 
came  to  be  called  silent  discharge.  Here  at  the 
very  beginning  of  Franklin's  electrical  work  was 
the  embryo  lightning  rod. 

Of  all  the  startling  discoveries  following  close 
upon  that  of  the  Ley  den  jar  none  appeared  more 
incredible  to  the  English  scientists  than  that  Ameri- 
can colonists,  amid  the  urgencies  of  their  assumed 
vocations  of  hewing  down  the  forest  and  the 
Indians,  could  find  time  and  ability  to  make  genuine 
contributions  to  the  knowledge  of  Electricity.  In 
[26] 


The  American  Prometheus 

consequence,  the  reality  of  the  silent  discharge  phe- 
nomenon was  disputed  on  every  hand,  the  contro- 
versy growing  more  and  more  acrimonious  until  at 
the  time  the  Revolutionary  War  broke  out,  King 
George  himself  issued  a  decree  that  the  points  be 
removed  from  the  newly  erected  lightning  conduc- 
tors and  ball  tips  substituted.  Science  must  be  gov- 
erned by  loyalty  and  in  such  a  crisis  it  was  evident 
that  all  colonial  ideas  must  be  wrong.  But  in 
the  meantime  Franklin  had  secured  the  respectful 
attention  of  the  scientific  world. 

His  interest  had  been  excited  by  reading  of  the 
experiments  which  Dr.  Watson  had  made  in  dis- 
charging a  Ley  den  jar  through  a  wire  laid  over 
Westminster  bridge.  Three  observers  had  been 
used ;  one  standing  on  the  bank  of  the  Thames  and 
grasping  in  one  hand  an  iron  rod  which  dipped 
in  the  water  while  he  held  the  jar  in  the  other;  a 
second  observer  presenting  his  knuckle  to  the  knob 
of  the  jar  and  retaining  the  near  end  of  the  wire; 
and  the  third  standing  on  the  farther  bank  holding 
the  other  end  of  the  wire  and  another  iron  rod 
dipping  in  the  river.  All  three  men  got  a  severe 
shock  when  the  jar  discharged,  the  circuit,  as  Dr. 
Watson  christened  the  path  of  the  discharge,  con- 
sisting of  the  three  observers,  the  two  iron  rods,  the 
wire,  and  the  river.  The  doctor  soon  found  that 
the  earth  could  be  used  instead  of  water  for  the 
[27] 


Electricity:   Its  History  and  Development 

return  path,  and  thus  succeeded  in  transmitting  a 
shock  over  a  wire  to  a  point  two  miles  distant.  The 
idea  of  signaling  by  this  means  did  not  occur  to 
him,  although  his  discovery  of  the  earth  return  was 
an  important  step  toward  telegraphy. 

Watson  was  much  more  interested  in  explaining 
the  results  than  in  finding  a  practical  application, 
however,  and  developed  a  complex  theory  of  elec- 
tricity which  was  little  more  than  published  when  an 
account  of  Franklin's  "  one  fluid  "  theory  was  read 
to  the  Royal  Society.  According  to  Franklin's 
idea  all  bodies  in  the  normal  state  contain  a  certain 
definite  amount  of  the  "  electric  fire,"  or  electric 
fluid,  and  are  in  equilibrium.  If  by  any  means  this 
amount  is  increased  in  a  given  body,  that  body 
becomes  charged  positively,  or  -f-  ;  if  on  the  other 
hand  the  normal  amount  is  decreased,  the  body 
becomes  — ,  or  negatively  charged.  If  a  body  in 
either  condition  approaches  one  in  the  normal 
uncharged  state,  a  spark  passes,  equalizing  the  dis- 
tribution of  the  total  amount,  this  spark  becoming 
more  vigorous  as  the  difference  in  amount  becomes 
greater.  Hence  it  is  most  violent  between  a  highly 
electrified  positive  and  a  highly  charged  negative 
body.  This  theory  is  probably  no  nearer  the  physi- 
cal truth  than  the  "  two  fluid  "  theory  of  Du  Fay, 
but  it  gives  the  clearest  and  simplest  conception  of 
the  observed  relations,  and  so  has  maintained  a 
[28] 


The  American  Prometheus 

leading  popular  position  ever  since  Franklin 
proposed  it. 

With  a  mind  cleared  by  his  theory,  Franklin 
immediately  observed  that  when  charged  from  a 
glass-globe  electrical  machine,  the  inner  coating  of 
the  Ley  den  jar  connected  to  the  machine  was  -[-, 
and  the  outer  coating  — ,  and  he  proceeded  to  make 
a  form  of  jar  which  could  be  easily  taken  apart,  in 
order  to  find  just  where  the  electricity  was  stored. 
For  this  purpose  he  used  a  pane  of  glass  with  sheets 
of  lead  on  opposite  sides,  and  discovered  that  the 
electricity  was  not  in  the  coatings  but  was  on  the 
surfaces  of  the  glass,  held  or  bound  there  by  the 
attraction  of  opposite  electrifications  until  a  path 
was  provided  by  which  the  -|-  and  —  charges  could 
reunite.  Again  the  European  theory  was  contro- 
verted. All  observers  had  supposed  the  electricity 
to  be  contained  in  the  water,  iron  filings,  or  lead 
plate  used  to  fill  the  jar,  and  it  took  some  time  for 
them  to  accept  Franklin's  view  that  these  coatings 
merely  served  to  conduct  the  charge  to  the  inner 
surface  of  the  glass,  while  an  equal  charge  was 
conducted  away  from  the  outer  surface  by  the  ex- 
terior coating.  But  truth  was  with  Franklin,  and 
his  explanation  gradually  displaced  all  others. 

Evidently,  if  the  electricity  was  stored  on  the 
surface  of  the  glass,  the  quantity  of  the  charge 
which  a  jar  could  hold  would  be  increased  in  pro- 
[29] 


Electricity:   Its  History  and  Development 

portion  to  the  surface,  and  two  jars  with  the  two 
outer  and  two  inner  coatings  connected  would  hold 
twice  the  charge,  or  have  twice  the  capacity  of  a 
single  jar. 

Franklin  verified  this  discovery  by  experiment 
and,  by  increasing  the  number  of  jars  to  six  or 
more,  evolved  what  he  called  an  electric  battery 
which  gave  a  sufficiently  powerful  discharge  to  kill 
a  turkey  weighing  ten  pounds.  The  arrangement 
of  jars  so  that  all  the  inner  coatings  were  connected 
together,  as  were  all  the  outer  coatings,  making  a 
combination  equivalent  to  a  single  large  jar,  he 
called  the  parallel  connection;  while  he  named  the 
connection  cascade  when  the  outer  coating  of  the 
first  was  connected  to  the  inner  coating  of  the  sec- 
ond, the  outer  coating  of  the  second  to  the  inner 
coating  of  the  third,  etc. ;  so  that  in  charging,  as 
he  says,  "  What  is  driven  out  of  the  tail  of  the  first, 
serves  to  charge  the  second  and  so  on."  This  ar- 
rangement of  electrical  devices  in  symmetrical  suc- 
cession giving  a  single  path  for  the  electric  flow  is 
now  called  the  series  connection,  but  Franklin's  term 
"parallel"  is  still  used  for  an  arrangement  which 
offers  simultaneous  paths. 

Early  in  his  experiments,  Franklin  was  struck 

with  the  similarity  between  the  electric  spark  and 

the  lightning  flash.     Others  had  remarked  this,  but 

it  remained  for  the  Philadelphia  printer  to  analyze 

[30] 


Leyden  jars  connected  in  series 


Leyden  jars  connected  in  parallel 


An  early  form  of  trough  battery  containing  twenty-seven 
"cells"  in  series  [Page  ^0 


The  American  Prometheus 

the  points  of  similarity  and  supply  the  proof  of 
identity.     In  1749  he  wrote: 

The  electric  fluid  agrees  with  lightning  in  these  par- 
ticulars: (1)  Giving  light;  (2)  color  of  the  light;  (3) 
crooked  direction;  (4)  swift  motion;  (5)  being  conducted 
by  metals;  (6)  crack  or  noise  in  exploding;  (7)  rending 
bodies  it  passes  through;  (8)  destroying  animals;  (9)  melt- 
ing metals;  (10)  firing  inflammable  substances,  and  (11) 
sulphurous  smell.  The  electric  fluid  is  attracted  by  points; 
we  do  not  know  whether  this  property  is  in  lightning. 
But  since  they  agree  in  all  the  particulars  wherein  we 
can  already  compare  them,  is  it  not  probable  that  they 
agree  likewise  in  this?  Let  the  experiment  be  made. 

A  year  later  he  outlined  the  necessary  experiment 
in  a  letter  to  his  English  friend  Collinson. 

On  the  top  of  some  high  tower  or  steeple,  place  a  kind 
of  sentry  box  —  big  enough  to  contain  a  man  —  and  an 
electrical  stand"  [a  stool  with  feet  made  of  glass  or  other 
insulating  material,  so  that  any  one  standing  thereon  is 
insulated  from  the  ground].  "From  the  middle  of  the 
stand  let  an  iron  rod  rise  and  pass,  bending  o'ut  of  the 
door,  and  then  upright  20  or  30  feet,  pointed  very  sharp 
at  the  end.  If  the  electrical  stand  be  kept  clean  and  dry, 
a  man  standing  on  it,  when  such  clouds  are  passing  low, 
might  be  electrified  and  afford  sparks,  the  rod  drawing 
fire  to  him  from  the  cloud. 

With  the  idea  of  the  necessity  of  a  high  tower  or 
steeple  in  mind  Franklin   cleverly   started  a  sub- 
scription to  build  such  a  steeple  on  the  Philadelphia 
meeting  house.     Contributions  were  slow,  however, 
[31] 


Electricity:   Its  History  and  Development 

and  in  the  meantime  his  letters  to  Collinson  were 
published  in  England  and  quickly  translated  and 
reprinted  in  France,  where  the  proposed  lightning 
experiment  attracted  immediate  attention. 

In  the  spring  of  1752  three  French  philosophers, 
d'Alibard,  de  Lor,  and  de  Buffon,  erected  iron  rods 
over  their  houses  or  in  their  gardens,  and  all  suc- 
ceeded in  drawing  vigorous  sparks  from  the  rods 
during  local  thunderstorms.  With  characteristic 
enthusiasm  the  results  were  immediately  communi- 
cated to  the  French  Academy  and  the  identity  of 
lightning  and  electricity  proclaimed,  due  credit  be- 
ing given  to  Franklin.  But  when  the  news  reached 
him  he  was  not  satisfied;  for  none  of  the  French 
experiments  had  been  made  from  a  high  steeple, 
and  the  ends  of  the  rods  must  have  been  far  from 
the  clouds.  Unfortunately  his  own  steeple  project 
continued  to  mature  very  slowly,  and  there  were 
no  high  hills  near  Philadelphia;  but  after  much 
pondering  upon  the  necessity  of  getting  nearer  the 
clouds  he  conceived  the  famous  kite  experiment.  In 
his  own  words : 

Make  a  small  cross  of  two  strips  of  cedar,  the  arms 
so  long  as  to  reach  to  the  four  corners  of  a  large  thin  silk 
handkerchief  when  extended;  tie  the  corners  of  the  hand- 
kerchief to  the  extremities  of  the  cross,  so  you  have  the 
body  of  a  kite,  which  being  properly  accommodated  with 
a  tail,  loop,  and  string,  will  rise  in  the  air,  like  those 
made  of  paper;  but  this,  being  of  silk,  is  fitter  to  bear 

[32] 


The  American  Prometheus 

the  wet  and  wind  of  a  thundergust  without  tearing.  To 
the  top  of  the  upright  stick  is  to  be  fixed  a  very  sharp- 
pointed  wire,  rising  a  foot  or  two  above  the  wood.  In 
the  end  of  the  twine,  next  the  hand,  is  to  be  held  a  silk 
ribbon,  and  where  the  silk  and  cord  join  a  key  may  be 
fastened.  This  kite  is  to  be  raised  when  a  thundergust 
appears  to  be  coming  on,  and  the  person  who  holds  the 
string  must  stand  within  a  door  or  window,  or  under  some 
cover,  so  that  the  silk  ribbon  may  not  be  wet;  and  care 
must  be  taken  that  the  twine  does  not  touch  the  frame  of 
the  door  or  window.  As  soon  as  any  of  the  thunder- 
clouds come  over  the  kite,  the  pointed  wire  will  draw  the 
electric  fire  from  them,  and  the  kite  with  all  the  twine  will 
be  electrified,  and  the  loose  filaments  of  the  twine  will 
stand  out  every  way  and  be  attracted  by  an  approaching 
finger.  And  when  the  rain  has  wetted  the  kite,  so  that  it 
can  conduct  the  electric  fire  freely,  you  will  find  it 
stream  out  plentifully  from  the  key  on  the  approach  of 
your  knuckle.  At  this  key  the  phial  may  be  charged,  and 
from  electric  fire  thus  obtained  spirits  may  be  kindled  and 
all  the  other  electric  experiments  be  performed  which  are 
usually  done  by  the  help  of  a  rubbed  glass  globe  or  tube, 
and  thereby  the  sameness  of  the  electric  matter  with  that 
of  lightning  completely  demonstrated. 

Today  theory  admits  but  little  difference  between 
this  experiment  made  by  Franklin  in  175&  and  the 
rod  experiments  performed  by  the  French  philos- 
ophers, but  to  the  world  of  the  eighteenth  century 
it  appeared  much  more  conclusive. 

By  continuing  the  rod  to  the  earth,  the  "end 

being  three  or  four  feet  in  moist  ground,"  Franklin 

produced  the  lightning  rod.     He  realized  clearly 

the  two  functions  of  such  a  rod:  first,  discharging 

[33] 


Electricity:   Its  History  and  Development 

a  slowly  approaching  cloud  by  equalizing  its  charge 
with  that  of  the  great  earth  reservoir  through  the 
phenomenon  of  the  silent  discharge  from  points, 
as  in  the  case  of  the  cannon  ball ;  and  second,  that 
of  directing  and  conducting  the  electric  discharge 
when  the  approach  of  the  cloud  was  so  rapid  or  the 
charge  so  great  that  a  spark  or  flash  of  lightning 
passed  before  the  silent  discharge  could  equalize  the 
electrical  condition.  Apparently  then,  he  must 
have  appreciated  the  great  danger  of  the  experi- 
ments with  rods  and  kites  which  soon  began  to  be 
repeated  in  different  parts  of  Europe.  In  either 
test  the  conducting  path  terminated  at  some  dis- 
tance from  the  ground,  and  a  direct  stroke  of  light- 
ning must  inevitably  jump  from  the  terminal  to 
the  nearest  good  conductor,  which  was  most  likely 
to  be  the  body  of  the  observer.  This  danger  was 
sadly  proved  by  the  fate  of  Prof.  Richmann  of  the 
University  of  St.  Petersburg,  who  in  1753  was 
struck  dead  by  such  a  lightning  bolt  from  his 
experimental  rod. 

For  some  time  Prof.  Richmann's  death  was  used 
as  an  argument  against  the  lightning  conductor, 
but  the  difference  betwen  the  well  grounded  rod 
offering  the  best  direct  path  to  earth  and  the  incom- 
plete path  of  the  experimental  rod  was  gradually 
appreciated  and  Franklin's  invention  was  univer- 
sally accepted  as  almost  perfect  protection  against 
[34] 


The  American  Prometheus 

the  dreaded  lightning.  Modern  conditions,  the  net- 
work of  wires  in  and  around  our  cities,  the  closely 
set  masses  of  building,  and  the  myriad  poles  rising 
to  considerable  heights,  have  largely  reduced  the 
lightning  hazard  in  the  more  thickly  settled  re- 
gions ;  but  for  isolated  buildings  the  lightning  rod 
installed  according  to  improved  methods  suggested 
by  Sir  Oliver  Lodge  is  still  the  best  protection. 

In  this  proof  of  the  identity  of  the  electric  spark 
and  the  lightning  flash,  and  in  the  invention  of  the 
lightning  conductor,  the  world  gained  the  first 
practical  results  of  electrical  investigation.  A  cen- 
tury and  a  half  had  passed  since  Gilbert  offered 
work  of  equal  value  in  magnetism,  but  even  so  the 
pace  of  real  advance  was  quickening,  and  the  dawn 
of  the  century  of  electricity  was  almost  at  hand. 
For  a  decade  the  friction  experiments  and  kite  rais- 
ings were  repeated,  with  slight  modifications  but  no 
improvements  of  moment ;  and  then,  suddenly,  with 
an  apparently  irrelevant  discovery  of  Galvani,  was 
opened  an  entirely  new  field  for  fundamental 
pioneering. 


[35] 


Ill 


THE  CONVULSED  FROG-LEG  AND  WHAT 
CAME  OF  IT 

OMETIME  in  the  latter  half  of  the  eighteenth 
century  (the  date  usually  taken  is  1786)  it 
chanced  that  Aloisio  Galvani,  professor  of  anatomy 
in  the  University  of  Bologna,  was  preparing  for 
some  electrical  experiments  in  his  laboratory  while 
an  assistant  was  completing  the  dissection  of  a 
frog.  Numerous  sparks,  jumping  across  the  ter- 
minals of  an  electrical  machine  near  the  frog,  pro- 
duced no  unusual  result,  but  suddenly  the  assistant 
was  astounded  by  the  violent  convulsions  of  one  of 
the  dismembered  frog's  legs  which  he  chanced  to 
be  touching  with  his  scalpel  just  at  the  instant 
another  spark  occurred  in  the  machine.  Galvani 
immediately  became  interested,  had  the  experiment 
repeated  many  times,  and  finally  came  to  the  con- 
clusion that  the  convulsion  was  undoubtedly  due  to 
electricity.  Strange  to  say,  however,  he  believed 
that  as  convulsions  could  be  produced  by  properly 
manipulating  the  scalpel  even  when  no  spark  dis- 
charge took  place,  the  electricity  must  be  generated 
[36] 


The  Convulsed  Frog-Leg 

in  the  frog-leg  itself  at  the  internal  junctions  of 
nerves  and  muscles,  and  was  discharged  by  the 
contact  made  through  the  blade  between  the  ex- 
posed muscle  and  the  nerve  ends.  Indeed,  he 
thought  for  some  time  that  in  this  "  animal  elec- 
tricity," as  he  called  it,  he  had  discovered  the  vital 
force  which  animates  our  otherwise  lifeless  bodies, 
and  his  first  published  description  of  his  experi- 
ments presents  this  theory.  Unfortunately  for 
biology  today  that  particular  "vital  force"  still 
remains  to  be  discovered;  but  Galvani's  work 
started  a  series  of  discoveries  resulting  in  our  mod- 
ern generation  of  electricity,  the  vital  force  of  the 
twentieth  century. 

Most  prominent  among  the  persons  attracted 
by  Galvani's  papers  was  his  fellow  countryman, 
Alessandro  Volta,  Professor  of  Physics  at  the 
University  of  Pavia.  Volta  had  already  made  an 
important  contribution  to  electrical  science  in  his 
invention  of  the  electrophorus,  a  simple  apparatus 
consisting  of  a  cake  of  resin  to  be  electrified  by 
friction,  and  a  disc  of  metal  on  an  insulating 
handle  which  could  be  charged  by  induction  an 
indefinite  number  of  times  from  one  electrification 
of  the  resin  cake.  The  electrophorus  was  much 
easier  to  make  than  the  rotating  electrical  machines 
and  would  operate  successfully  in  damp  weather; 
so  it  was  extensively  used  for  charging  Leyden 
[37] 


Electricity:   Its  History  and  Development 

jars  and  still  remains  one  of  the  most  satisfactory 
pieces  of  apparatus  easily  constructed  by  the 
embryo  electrical  pioneer. 

Volta  at  first  accepted  Galvani's  theory  of  ani- 
mal electricity,  but  after  a  long  series  of  experi- 
ments he  found  that  not  only  were  the  convulsions 
of  the  frog-leg  much  more  violent  when  the  con- 
ductor between  nerves  and  muscles  was  made  up  of 
two  wires  of  different  metals  twisted  together  at 
one  pair  of  ends,  the  other  pair  being  used  for  the 
two  contact  points,  as  Galvani  had  observed,  but 
also  the  violence  of  the  convulsions  depended 
largely  on  what  particular  metals  were  paired. 
From  the  last  observation  Volta  developed  his 
theory  that  the  electricity  was  generated  at  the 
contact  of  the  dissimilar  metals  and  proceeded  to 
develop  the  remarkable  instrument  now  called  the 
voltaic  pile,  of  which  Arago  wrote :  "  Volta's  pile, 
the  most  wonderful  apparatus  that  has  ever  come 
from  the  hand  of  man,  not  excluding  even  the 
telescope  or  the  steam  engine." 

The  pile,  which  was  first  exhibited  in  1800,  con- 
sisted of  a  series  of  discs  of  silver,  zinc,  and  cloth 
moistened  with  salt  water,  each  about  an  inch  in 
diameter,  piled  up  in  a  column  until  the  desired 
number  were  assembled  in  regular  order,  for  ex- 
ample, silver,  zinc,  cloth,  silver,  zinc,  cloth.  In 
Volta's  own  words  this  resulted  in  "the  construe- 
[38], 


lU   SILVER. 


Volta's  pile,  the  first  generator  of  a  continuous  electrical 
current 


The  "crown  of  cups"  devised  by  Volta  to  overcome  the 
evaporation  of  the  electrolyte  in  his   pile 

[Page  40 


The  Convulsed  Frog-Leg 

tion  of  an  apparatus  which  resembles,  so  far  as  its 
effects  are  concerned  (that  is,  by  the  commotion  it 
is  capable  of  making  one  feel  in  the  arms,  etc.), 
the  Leyden  batteries,  and  still  more  the  fully 
charged  electric  batteries.  It  acts,  however,  with- 
out ceasing,  and  its  charge  reestablishes  itself  after 
each  explosion.  It  operates,  in  a  word,  by  an 
indestructible  charge,  by  a  perpetual  action  or 
impulse  on  the  electric  fluid."  Furthermore,  the 
"  commotion "  was  directly  proportionate  to  the 
number  of  plates.  A  single  pair  produced  no  ap- 
parent effect  in  the  arms,  though  when  the  two 
discs  were  separated  by  the  tongue  and  the  outer 
edges  touched,  a  peculiar  sour  taste  was  experi- 
enced ;  but  one  hundred  pairs  gave  a  distinct  "  com- 
motion "  and  five  hundred  pairs  a  very  painful  one. 
The  most  notable  characteristic  of  the  new  ap- 
paratus was  the  continuity  of  the  electric  discharge 
in  comparison  with  that  from  a  Leyden  jar.  Fol- 
lowing up  the  idea  of  an  electric  fluid,  this  con- 
tinuous discharge  was  easily  conceived  as  a  flow  of 
electricity,  or  as  we  say  today,  a  continuous  electric 
current.  The  continuity  was  soon  found,  how- 
ever, to  be  strictly  limited.  If  the  end  plates  of 
a  pile  were  connected  through  a  wire,  as  the  mois- 
ture in  the  cloth  discs  evaporated  the  current  be- 
came smaller  and  finally  in  a  few  hours,  when  the 
cloth  was  dry,  ceased  entirely.  To  overcome  this 
[39] 


Electricity:   Its  History  and  Development 

difficulty  Volta  devised  his  "  crown  of  cups,"  the 
cloth  discs  being  replaced  with  glass  cups  filled  with 
salt  water  and  the  metal  discs  with  strips  of  silver 
and  zinc. 

In  Volta's  arrangement  the  silver  in  one  cup  was 
connected  to  the  zinc  in  the  adjacent  cup,  the 
silver  in  this  to  the  zinc  in  the  next,  and  so  on,  the 
series  thus  beginning  with  the  zinc  of  the  first  cup 
and  ending  with  the  silver  of  the  last.  From 
analogy  with  the  Ley  den  jar  battery  the  arrange- 
ment was  called  the  series  connection  of  a  battery 
of  cups.  Attempts  were  made  to  secure  greater 
convenience  by  using  a  single  trough  divided  into 
cells  by  plates  formed  of  sheets  of  zinc  and  silver 
soldered  face  to  face  and  cemented  into  grooves  cut 
at  regular  distances  in  the  trough  sides.  But  these 
cells  were  difficult  to  clean  and  persisted  in  leaking, 
so  that  the  scheme  was  abandoned,  though  the 
name  cell  has  been  retained  and  applied  to  the  unit 
jar  and  its  contents  in  place  of  the  term  cup. 

In  the  course  of  these  early  experiments  several 
important  facts  were  noted.  First,  it  was  found 
that  the  action  was  more  vigorous  if  the  water  in 
the  cells  was  replaced  with  weak  sulphuric  acid ;  but 
then  the  zinc  was  rapidly  dissolved  even  when  no 
current  was  taken  from  the  cell,  hydrogen  gas 
being  given  off  at  the  zinc.  To  lessen  the  waste 
thus  caused  the  cells  were  arranged  in  a  plunge 
[40] 


The  Convulsed  Frog-Leg 

battery,  the  metal  strips  or  plates  being  attached 
to  a  frame  so  that  all  could  be  lifted  out  of  the 
acid  when  the  battery  was  not  in  use.  This  waste 
could  be  practically  stopped,  however,  even  when 
the  plates  were  left  immersed  by  rubbing  the  zinc 
with  mercury  or  amalgamating  it  before  assembling 
the  cells,  and  with  this  improvement  the  way  was 
cleared  for  a  new  theory  of  the  action  of  the  cell. 
For  now,  although  practically  no  gas  was  evolved 
from  the  cells  when  no  current  was  taken  from 
them,  a  copious  stream  of  gas  appeared  as  soon  as 
a  circuit  was  completed  between  the  end  plates,  and 
the  zinc  was  consumed  in  proportion  to  the  elec- 
tricity used. 

Was  it  not  likely  that  the  current  of  electricity 
was  due  not  to  the  contact  of  the  silver  and  zinc 
strips  in  adjacent  cells,  but  to  some  chemical  action 
between  the  silver  and  zinc  strips  and  the  liquid  or 
electrolyte  used  in  each  cell?  All  the  investigators 
recognized  that  somewhere  in  the  circuit  a  force 
was  produced  capable  of  moving  electricity  through 
a  closed  path.  The  cells  were  indeed  often  called 
"  electro-motors "  or  electricity  movers,  and  the 
force  was  called  electricity-moving  force  or  "  elec- 
tro-motive force"  terms  still  in  use  today.  True, 
the  meaning  of  "  electro  motor "  has  gradually 
changed,  until  it  is  now  almost  always  used  to 
indicate  a  device  for  producing  mechanical  motion 
[41] 


Electricity:   Its  History  and  Development 

from  electricity,  but  electro-motive  force,  generally 
abbreviated  to  e.  m.  f.,  is  in  constant  use  in  our 
modern  nomenclature  in  its  exact  original  sense. 

All  scientists,  then,  were  agreed  as  to  the  exist- 
ence of  an  electro-motive  force  in  the  cell  circuit; 
but  as  soon  as  the  possibility  of  the  chemical  origin 
of  this  force  was  suggested  by  Fabroni  the  elec- 
trical world  divided  into  two  parties  —  one  assert- 
ing that  the  real  seat  of  force  was  at  the  junction 
of  dissimilar  metals  as  Volta  had  suggested;  the 
other,  that  the  force  was  produced  at  the  contact 
of  the  electrolyte  with  the  metal  plates,  or  elec- 
trodes. After  the  most  vigorous  and  voluminous 
controversy  which  has  ever  retarded  the  progress 
of  electrical  science,  the  chemical  theory  has  finally 
prevailed,  so  that  today  we  may  think  of  the  elec- 
tric current  as  produced  from  the  consumption  of 
zinc  in  a  cell,  much  as  a  current  of  air  is  produced 
in  the  inlet  and  outlet  pipes  of  an  otherwise  closed 
room  by  a  gas  flame  within.  With  the  acceptance 
of  the  chemical  theory,  too,  it  becomes  apparent 
that  the  convulsions  of  the  frog-legs  observed  by 
Galvani  were  generally  due  to  chemical  action  be- 
tween the  metallic  part  of  the  circuit  and  the 
juices  of  the  frog  tissues. 

But  entirely  apart  from  the  theory  of  the  voltaic 
cell  were  the  possible  practical  applications  of  elec- 
tricity which  might  be  found  if  a  source  of  a  really 
[42] 


The  Convulsed  Frog-Leg 

continuous  current  could  be  developed.  Even  with 
the  improvements  in  amalgamation  and  cell  con- 
struction, however,  the  current  from  a  simple  cell 
rapidly  decreased  in  strength.  After  much  re- 
search this  was  finally  traced  to  the  accumulation 
of  hydrogen  gas  at  the  copper  plate,  which  pro- 
duced an  e.  m.  f .  opposing  the  original  e.  m.  f .  of 
the  cell,  and  which  also  obstructed  the  flow  of  cur- 
rent with  a  partially  insulating  layer  of  gas 
bubbles.  A  cell  in  this  condition  is  said  to  be 
polarized  and  most  of  the  modifications  of  the 
original  design  have  been  made  in  the  attempt  to 
get  the  hydrogen  out  of  the  way  and  allow  the  cell 
to  furnish  current  until  the  zinc  is  consumed.  One 
of  the  most  successful  schemes  is  to  surround  the 
copper  plate,  or  the  carbon  plate  (which  is  fre- 
quently used  instead  of  copper)  with  some  chem- 
ical which  will  combine  with  the  hydrogen,  thus 
keeping  the  plate  free  from  gas.  This  method  is 
applied  in  the  Leclanche  cell  frequently  used  for 
ringing  bells.  Here  the  carbon  plate  is  packed  in 
a  mixture  of  manganese  dioxide  and  gas  carbon 
contained  in  a  porous  cylinder,  a  similar  arrange- 
ment being  used  in  most  of  the  dry  cells;  but 
although  the  manganese  dioxide  serves  to  depolarize 
the  cell,  the  action  is  slow,  and  this  class  of  bat- 
teries can  be  used  only  for  intermittent  service, 
where  considerable  periods  of  rest  permit  the  de- 
[43] 


Electricity:   Its  History  and  Development 

polarizing  agent  to  act.  In  the  Edison-Lalande 
and  Gravity  cells  the  materials  are  so  arranged  that 
the  action  of  the  depolarizer  produces  metallic  cop- 
per which  is  deposited  on  the  copper  electrode,  thus 
keeping  the  copper  surface  fresh  and  obviating  any 
obstruction  of  the  current  by  waste  products.  The 
depolarizing  action  in  these  cells  is  so  perfect  that 
batteries  will  furnish  almost  constant  current  con- 
tinuously until  the  zinc  is  used  up.  For  many 
years  the  Gravity  cell  supplied  the  current  for  the 
telegraph  systems  of  the  world.  But  zinc  is  at 
best  an  expensive  fuel;  and,  with  the  development 
of  electric  generators,  the  voltaic  cell,  or  primary 
battery  —  as  it  is  frequently  called  because  the  cur- 
rent results  directly  from  chemical  action  —  has 
been  relegated  to  those  uses  which  require  small 
currents  at  infrequent  intervals. 

Beside  the  idea  of  electro-motive  force,  the  vol- 
taic cell,  with  its  continuous  current,  created  the 
necessity  for  many  fundamental  conceptions  in 
electric  science.  Our  ultimate  idea  of  any  force  is 
that  of  a  pressure,  and  the  electro-motive  force  is, 
therefore,  conceived  as  an  electrical  pressure  tend- 
ing to  cause  an  electric  current  to  flow  in  any  con- 
tinuous or  closed  circuit.  If  the  path  is  broken  at 
any  point  the  pressure  still  exists,  but  no  current 
can  flow  as  long  as  the  path  is  an  open  circuit. 
Now  a  current  and  a  pressure  both  have  a  definite 
[44] 


The  Convulsed  Frog-Leg 

direction ;  and,  although  the  early  investigators  had 
no  experimental  ground  for  deciding  which  direc- 
tion the  current  from  a  battery  actually  took,  they 
called  the  copper  plate  the  positive  pole  of  the  bat- 
tery and  declared  that  the  current  should  be  con- 
sidered to  flow  in  the  external  circuit  from  this 
positive  pole  to  the  negative  pole  or  zinc  plate. 
Within  the  cell,  of  course,  the  flow  is,  therefore, 
represented  as  being  from  the  zinc  to  the  copper. 
As  the  current  is  necessarily  in  the  direction  of 
the  pressure,  the  e.  m.  f.  of  the  cell  is  taken  as 
being  toward  the  negative ;  or  ( since  in  the  older 
science  of  electric  charges  a  body  with  a  positive 
charge  was  said  to  have  a  higher  electrical  poten- 
tial, and  one  with  a  negative  charge  a  lower  poten- 
tial than  neutral  bodies)  the  positive  pole  of  a 
battery  is  declared  to  be  at  a  higher  potential  than 
the  negative  and  the  pressure  of  the  cell  taken  as 
the  potential  difference  between  the  poles.  When 
the  cell  is  on  an  open  circuit  the  pressure  or  poten- 
tial difference  at  its  terminals  is  identical  with  its 
e.  m.  f . ;  but  as  soon  as  a  current  is  allowed  to  flow, 
a  part  of  the  electro-motive  force  is  consumed  in 
forcing  the  current  through  the  electrodes  and 
electrolyte,  and  the  pressure  which  reaches  the 
terminals  is,  therefore,  less  than  the  true  e.  m.  f. 
Furthermore,  the  amount  of  e.  m.  f.  consumed 
depends  on  the  strength  of  current  which  flows ; 

[45] 


Electricity:   Its  History  and  Development 

and,  to  Volta  and  his  contemporaries,  the  relations 
between  current  strength  and  pressure  seemed  most 
confusing. 

But  the  confusion  was  only  apparent  —  the 
beautiful  simplicity  of  the  relations  was  soon  to  be 
demonstrated  in  such  final  form  by  Dr.  George 
Simon  Ohm  that  Ohm's  law,  as  it  is  called,  remains 
and  will  probably  always  remain  one  of  the  funda- 
mental expressions  of  our  understanding  of  elec- 
tricity. 


[46] 


IV 
"THE  ELECTRIC  CONFLICT" 

THROUGH  all  the  early  period  of  experiments 
upon  electricity  and  magnetism  some  relation 
between  these  two  mysterious  sciences  was  suspected. 
The  earliest  philosophers  indeed  believed  magnetic 
and  electric  attractions  to  be  identical,  and  even 
after  Dr.  Gilbert  had  shown  the  many  points  of 
difference  the  elements  of  similarity  were  striking. 
Furthermore,  each  advance  of  the  pioneers  brought 
to  light  some  new  fact  which  strengthened  the  sus- 
picion of  relation;  as,  when  Franklin  noted  that 
steel  objects  struck  by  lightning  were  sometimes 
found  to  be  strongly  magnetized,  and  that  a  steel 
needle  could  occasionally  be  magnetized,  though 
with  an  unpredictable  polarity,  by  discharging  a 
Ley  den  jar  along  its  axis.  Thus,  when  the  inven- 
tion of  the  voltaic  cell  was  announced,  the  new 
possibilities  of  discovering  the  relation  attracted 
various  experimenters.  Single  cells  were  suspended 
in  the  hope  that  each  would  come  to  rest  with  some 
definite  position  in  relation  to  the  points  of  the  com- 
pass; or  very  sensitive  compass  needles  were  used 

[47] 


Electricity:   Its  History  and  Development 

to  detect  any  magnetic  attraction  which  the  poles 
of  the  cells  might  possess.  But  all  these  experi- 
ments, performed  on  the  electric  charge  of  open- 
circuited  cells,  failed.  Accumulated  electricity  at 
rest  on  a  conductor  has  no  magnetic  effect. 

Among  the  men  especially  interested  in  estab- 
lishing the  suspected  relation  was  Hans  Christian 
Oersted,  professor  of  physics  in  the  University  of 
Copenhagen.  To  him  came  the  idea  that  perhaps 
some  effect  of  the  electric  current  on  the  magnetic 
needle  might  be  shown.  Dilating  on  his  pet  idea 
to  his  assembled  students  one  day  in  1819,  he 
chanced,  by  way  of  illustrating  his  remarks,  to  hold 
a  wire,  connecting  a  rather  powerful  battery  of  cells 
and  carrying,  therefore,  a  considerable  current,  just 
over  and  parallel  to  a  large  magnetic  needle  which 
had  come  to  rest  in  the  normal  position  on  the  lec- 
ture table.  Imagine  the  excited  delight  of  the  staid 
professor  and  his  students  when,  before  their  eyes, 
the  needle  slowly  swung  aside,  tending  toward  a 
position  at  right  angles  to  the  wire !  For  the  next 
few  weeks,  Oersted  devoted  himself  to  trying  the 
effect  of  all  possible  positions  of  the  wire  with  rela- 
tion to  the  needle.  If  he  reversed  the  direction  of 
the  current  the  needle  deflected  in  the  opposite 
direction;  if  the  current  direction  remained  un- 
changed but  the  wire  was  moved  from  above  to 
below  the  needle,  the  direction  of  deflection  also 
[48] 


Oersted's   original   experiment — the   magnetic    action   of 
"the  electric  conflict" 


Fig.   1.     The  multiplication  of  the  magnetic  effect  of  a 

current  by   a   winding   "turn" 


Fig.    2.      Ampere's   table 
and     coils     used      in   his 
A  electro- magnetic   discoveries 

(a)  Coil  showing  effect  of  earth's  field  on  a  current 

(b)  Coil  neutralizing  this  effect 

(c)  The  first  solenoid 


Fig.   3.      Lines   of  magnetic   force   from  two  permanent 
magnets  shown  by  iron  filings          [Page  53 


IS 

V&tiffi 

'r2Z?*3Zi7y>  •>'/"'•  '•  i ' 


^^^ — <=- 


(a)   Iron  filing  diagram  of  magnetic  lines  in  plane  per- 
pendicular to   axis   of   a   conducting  wire,  and    (b) 
relation    of    direction    of    movement    of    north 
magnetic  pole  to  direction  of  current  flow 

[Page  55 


"The  Electric  Conflict" 

reversed.  These  and  many  similar  facts  he  ob- 
served carefully  and  published  in  July,  1820,  under 
the  title  "  Experiments  on  the  effect  of  the  electric 
conflict  on  the  magnetic  needle." 

News  of  the  discovery  traveled  over  Europe  with 
remarkable  rapidity  and  everywhere  quickened 
scientific  interest  in  electricity.  Andre  Marie 
Ampere,  professor  of  mathematics  in  the  Ecole 
Polytechnique  of  Paris,  repeated  the  experiments 
carefully,  and  in  less  than  two  months  after  Oer- 
sted's publication,  presented  a  complete  theory  of 
the  phenomena.  His  first  result  was  the  famous 
rule  for  the  direction  of  movement  of  the  needle  in 
Oersted's  original  experiment.  "  Imagine  yourself 
swimming  in  the  wire  in  the  direction  of  the  current 
and  facing  the  needle,  then  the  north  pole  will  be 
deflected  toward  your  left  hand."  From  this  rule 
it  is  evident  that  if  the  wire  is  bent  over  and  back 
beneath  the  needle  so  as  to  form  a  rectangle,  as  in 
Figure  1,  the  effect  of  the  current  in  the  lower  side 
is  added  to  that  in  the  upper,  and  about  one-half 
the  current  will  produce  as  much  effect  as  the  total 
current  in  the  original  experiment.  By  continuing 
the  process  and  carrying  the  wire  say  ten  times 
around  the  needle,  or  making  a  winding  of  ten 
complete  turns,  one-twentieth  of  the  original  cur- 
rent will  produce  the  same  deflection ;  and  so  on  for 
greater  numbers  of  turns.  In  this  device,  invented 
[49] 


Electricity:   Its  History  and  Development 

by  Schweigger  in  1820,  we  have  available  a  very 
sensitive  means  of  detecting  or  measuring  almost 
infinitesimal  currents  of  electricity.  It  was  called 
at  first  a  "  multiplier  "  from  its  action  in  multiply- 
ing the  magnetic  effect  of  any  given  current;  as 
the  instrument  was  improved,  however,  and  came  to 
be  used  for  measurements  it  was  renamed  the  gal- 
vanometer, and  in  this  guise  it  is  one  of  the  most 
important  of  electrical  measuring  instruments. 

But  Ampere's  contribution  to  electricity  did  not 
stop  with  his  "  swimmer "  rule.  After  verifying 
Oersted's  work  he  began  original  investigation.  If 
the  current  caused  a  pivoted  magnet  to  move,  why 
should  not  a  magnet  move  the  current,  why  should 
not  the  magnetic  earth  move  a  conducting  wire? 
To  test  this  he  constructed  the  wire  rectangle 
shown  in  Figure  2A,  which  could  be  supported 
through  conducting  contacts  in  mercury  cups  so  as 
to  turn  freely  about  its  axis.  When  the  plane  of 
the  rectangle  was  placed  parallel  to  the  normal 
direction  of  the  compass-needle  and  a  current  sent 
through  the  wire,  the  rectangle  immediately  turned 
to  an  east  and  west  position;  and,  when  a  magnet 
was  held  near  it,  it  behaved  as  though  the  face  of 
the  rectangle  toward  the  north  were  a  north  mag- 
netic pole,  and  that  toward  the  south  a  south 
magnetic  pole. 

The  next  step  was  almost  self-evident,  for,  if  a 
[50] 


"The  Electric  Conflict'3 

current  affected  the  magnet  and  the  magnet  affected 
another  current,  evidently  one  current  should  affect 
another.  As  his  first  rectangle  was  controlled  by 
the  earth's  magnetism,  however,  Ampere  prepared  a 
double  rectangle,  shown  in  Figure  2B,  in  which 
the  two  halves  were  influenced  equally  but  in  oppo- 
site directions  by  the  earth,  and  which,  therefore, 
was  entirely  free  to  turn  under  the  influence  of  any 
magnetic  body  affecting  one  side  more  than  the 
other.  With  this  and  a  current-carrying  wire 
which  could  be  held  parallel  to  one  side  of  the 
double  rectangle,  Ampere  made  his  cardinal  dis- 
covery: that  currents  in  opposite  directions  repel, 
and  currents  In  the  same  direction  attract  each 
other.  Taking  these  experiments  as  a  basis  he 
developed  his  theory  that  magnetism  is  always  the 
result  of  currents  of  electricity  caused  by  unknown 
forces  to  flow  around  the  circumference  of  the  indi- 
vidual particles  of  which  the  magnet 'is  composed 
—  a  theory  especially  important  because  it  led  him 
to  construct  the  long  spiral  coil  of  wire  called  a 
solenoid,  shown  in  Figure  2C,  which,  when  sus- 
pended from  the  mercury  cups  and  connected 
to  a  battery,  exhibited  all  the  characteristics  of  a 
magnet. 

The  importance  of  the  solenoid  became  evident 
in  1825  when  Sturgeon  found  that  a  cylindrical 
bar  of  iron  placed  within  it  acquired  a  magnetic 
[51] 


Electricity:   Its  History  and  Development 

strength  many  hundred  times  that  of  the  solenoid 
alone,  and  that  when  the  current  ceased,  the  mag- 
netism of  the  core  disappeared.  Magnetism  under 
control  —  brought  into  existence  by  the  mere  clos- 
ing of  a  battery  circuit,  and  instantaneously  de- 
stroyed when  the  circuit  was  opened  —  magnetic 
attraction  easily  produced  even  as  early  as  1830  in 
such  strength  that  a  60-pound  magnet  wound  with 
700  feet  of  wire  and  supplied  by  a  few  cells  of 
battery  could  support  a  ton  weight' — entirely 
changed  the  possible  future  of  electricity.  These 
electro-magnets,  as  the  cored  solenoids  were  chris- 
tened by  Sturgeon,  at  once  took  a  place  in  nearly 
every  new  electrical  development,  and  today  are 
vital  parts  of  practically  all  electrical  apparatus. 

The  polarity  of  an  electro-magnet  is  at  once 
known  by  applying  Ampere's  rule  if  the  core  is 
considered  the  magnetic  needle.  Facing  the  core 
and  swimming  with  the  current,  the  north  pole  will 
be  found  to  the  left.  Perhaps  a  simpler  rule  to 
remember  is  that  when  facing  the  south  pole  the 
current  is  flowing  around  the  core  in  a  direction 
similar  to  the  movement  of  the  hands  of  a  clock  — 
or  in  a  clockwise  direction. 

So  much  for  the  observed  results.  But  how  can 
we  conceive  of  the  action  which  causes  them  ?  How 
does  a  current  flowing  through  a  wire  spiral  make 
a  magnet?  and  how  does  that  magnet  attract 

[52], 


"The  Electric  Conflict" 

iron?  Michael  Faraday,  the  greatest  of  English 
physicists,  attacked  these  problems  in  1830,  and 
with  his  lines  of  force  succeeded  in  producing  a 
theory  which,  although  it  does  not,  of  course,  tell 
us  what  magnetism  really  is,  is  such  a  simple 
method  of  accounting  for  all  the  phenomena  that 
it  forms  the  easiest  way  of  remembering  the  facts. 
In  the  sixteenth  century,  and  perhaps  even 
earlier,  it  had  been  observed  that  if  a  magnet  were 
covered  with  a  thin  smooth  board  or  other  stiff  sheet 
of  non-magnetic  material  and  then  fine  iron  filings 
sprinkled  on  the  sheet,  the  filings  arranged  them- 
selves in  very  definite  curved  lines  radiating  from 
the  two  poles  and  curving  around  until  the  lines 
from  opposite  poles  joined  as  in  the  region  below 
the  large  magnet  in  Figure  3.  Faraday  repeated 
this  experiment  with  almost  every  conceivable  modi- 
fication and  found  that  if  two  or  more  magnets 
were  used,  no  matter  what  their  relative  positions, 
the  lines  from  opposite  poles  always  tended  to  join 
and  those  from  similar  poles  to  repel  each  other. 
He  also  found  that  these  lines  represented  the  path 
which  a  north  pole  placed  at  any  point  on  the 
sheet  would  follow  in  moving  toward  the  south  pole 
of  the  principal  magnet  and  that  a  small  compass 
needle  pivoted  anywhere  on  the  sheet  took  up  a 
position  tangent  to  the  curve  of  the  line  passing 
through  the  pivot. 

[53] 


Electricity:    Its  History  and  Development 

The  space  surrounding  a  magnet,  then,  said 
Faraday,  may  be  best  thought  of  as  filled  with  in- 
visible lines  of  magnetic  force  starting  from  the 
north  pole,  curving  around  through  the  air  to  the 
south  pole,  and  returning  through  the  body  of 
the  magnet  again  to  the  north  pole.  These  lines 
are  in  tension  along  their  length  and  mutually  repel 
each  other.  Furthermore,  the  lines  travel  much 
more  easily  in  iron  than  in  air  and  try  to  crowd 
into  any  iron  placed  in  their  path.  Now,  anywhere 
that  a  line  enters  a  magnetic  substance  a  south 
pole  is  created,  while  a  north  pole  appears  at  the 
point  at  which  it  leaves;  hence  a  piece  of  iron 
placed  near  a  magnet  is  pulled  to  the  north  or 
south  pole  by  the  tension  along  the  lines  crowding 
into  it,  according  as  more  lines  point  directly 
toward  one  pole  or  the  other.  The  stronger  the 
magnet  the  more  lines  emerge  from  the  north  pole ; 
and  the  stronger  the  magnetic  effect  at  any  region 
in  space  the  more  lines  are  passing  through  that 
region.  Quite  a  resemblance  all  this  bears  to 
Robert  Norman's  "  sphere  of  vertue,"  but  in  place 
of  the  vague  ideas  of  Gilbert's  day,  Faraday  sees 
his  lines  of  force  threading  space,  acting  and  react- 
ing on  one  another  with  all  the  detail  of  a  reality. 

Applying  now  this  same  method  to  an  electrical 
conductor,  Faraday  again  found  his  lines  of  force, 
but  this  time  the  iron  filings  arranged  themselves 
[54] 


"The  Electric  Conflict" 

in  circles  around  the  conductor  in  a  plane  at  right 
angles  to  its  axis.  As  Oersted  had  predicted  the 
"  electric  conflict  acts  in  a  rotating  manner  " ;  and 
with  his  compass  Faraday  found  that  looking  along 
the  conductor  in  the  direction  of  the  current,  the 
lines  of  force  tended  to  move  a  north  pole  in  clock- 
wise rotation.  In  the  compass,  of  course,  the  south 
pole  tended  equally  to  anti-clockwise  rotation  so 
that  the  needle  merely  turned  until  tangent  to  the 
line  of  force  and  did  not  revolve  around  the  wire 
bodily.  But  Faraday  had  already  developed  an 
apparatus  in  which  the  current  affected  the  north 
pole  of  a  magnet  only,  and  had  thereby  produced 
continuous  rotation  of  the  magnet  —  the  first  elec- 
tric motor. 

When  Faraday  made  his  iron-filing  diagrams  on 
parallel  conductors  he  found  that  if  the  currents 
were  in  the  same  direction  the  adjacent  circular 
lines  of  force  tended  to  merge  into  a  single  line 
which,  because  of  the  tension  along  its  length, 
pulled  the  conductors  together;  while  if  the  cur- 
rents were  in  opposite  directions  the  repulsion  of 
similarly  directed  lines  of  force  caused  the  con- 
ductors to  separate.  From  B,  page  7£,  it  is  easily 
seen  that  as  current  flows  in  opposite  directions 
in  the  two  sides  of  a  loop,  the  lines  of  force  shown 
are  practically  those  from  one  turn  of  a  solenoid, 
and  hence  that  the  lines  of  force  outside  a  solenoid 
[55] 


Electricity:   Its  History  and  Development 

are  very  similar  to  those  outside  a  magnet,  while 
the  parallel  lines  inside  the  solenoid  are  exactly 
those  assumed  to  exist  within  a  magnet. 

The  cause  for  the  magnetic  effect  of  the  solenoid 
is  thus  apparent.  But  why  the  great  increase  in 
this  effect  when  a  soft-iron  core  is  inserted?  Mod- 
ern theory  accounts  for  this  by  assuming  each 
molecule  of  the  iron  to  be  a  natural  magnet. 
Normally  these  molecular  magnets  are  pointing 
heterogeneously  in  all  directions,  neutralizing  one 
another ;  but  when  placed  within  the  solenoid  in  the 
magnetic  field,  as  any  space  filled  with  lines  of 
force  is  called,  the  tiny  magnets  all  turn  easily  into 
line  like  compass  needles,  and  the  effect  of  all  the 
numberless  north  poles  is  added,  as  is  that  of  the 
south  poles,  producing  a  single  large  magnet  of 
great  strength.  As  soon  as  the  electric  current  is 
stopped  and  the  directing  field  of  force  removed, 
the  molecules  again  turn  haphazard  and  the  result- 
ant total  magnetism  is  zero.  In  the  case  of  harder 
material,  like  steel,  the  molecules  turn  with  greater 
difficulty,  and  once  in  line  retain  the  position  even 
after  the  electric  current  is  interrupted.  Thus 
steel  becomes  a  permanent  magnet  after  a  single 
magnetization. 

In  his  theory  of  magnetic  lines  Faraday  thus 
produced  a  tool  of  remarkable  power  for  electrical 
advance  —  a  power  which  he  used  almost  imme- 
[56] 


"The  Electric  Conflict" 

diately  to  develop  the  generation  of  electricity  in 
an  entirely  new  way,  and  thereby  to  make  electric 
science  the  main  ground  of  nineteenth-century 
progress. 


[57] 


AN  ANCHOR  RING  AND  WHAT  IT  HELD 


ONVERT  magnetism  into  electricity." 
Thus  briefly  Michael  Faraday  noted,  in  his 
laboratory  log  book  of  1822,  one  of  the  things 
he  thought  might  be  well  worth  doing.  He  could 
hardly  have  suspected  the  importance  of  the  task. 
Indeed  it  would  have  made  little  difference  could  he 
have  known  that  its  performance  was  to  place  him 
foremost  among  experimental  scientists  and  was  to 
furnish  the  essential  basis  of  the  most  marvelous 
practical  applications  of  electricity.  To  him  the 
mere  joy  of  the  discovery  of  scientific  truth  was 
quite  sufficient  incentive  and  reward. 

Four  times  in  the  course  of  nine  years  he  at- 
tacked the  problem  with  long  series  of  experiments, 
and  each  time  had  to  close  the  careful  record  of  his 
observations  with  the  words,  "  No  result."  But 
intuitively  he  seemed  to  know  that  a  solution  was 
possible.  A  current  flowing  in  a  wire  wound 
spirally  around  an  iron  bar  made  the  bar  a  power- 
ful magnet  —  why  did  not  a  magnet  in  a  coil  of 
wire  produce  a  current  in  that  wire?  All  his  ex- 
[58] 


Fig.  5.     Faraday's  anchor  ring  with  which  he  discovered 
the  induction  of  electric  current 

(By  special  permission   of  the    author  and   publishers   of  LT.    Fleming's   "Alternate 


Current    Transformer"    Vol.    I) 


Fig.    6.      The    first   electric   generator   producing   direct 
currents  [Pa-ge  62 


An  Anchor  Ring  and  What  It  Held 

periments  showed  emphatically  that  it  did  not  — 
still,  he  was  unconvinced.  During  this  period  he 
carried  a  small  model  of  an  electro-magnet  in  his 
pocket  and  in  leisure  moments  used  the  tiny  bar 
with  its  encircling  helix  of  insulated  copper  wire 
to  concentrate  his  attention  on  the  problem. 

In  the  summer  of  1831  for  the  fifth  time  he  be- 
gan to  experiment.  First  he  repeated  all  the 
experiments  of  his  contemporaries  which  could  pos- 
sibly aid  him  —  then  he  repeated  all  his  own  pre- 
vious experiments  and  then  —  he  struck  out  along 
a  new  line.  In  his  note  book  he  wrote : 

"  I  have  had  an  iron  ring  made  ( Figure  5 ) ,  iron 
round  and  %  of  an  inch  thick,  and  ring  6  inches 
in  external  diameter.  Wound  many  coils  of  cop- 
per round,  one-half  of  the  coils  being  separated  by 
twine  and  calico;  there  were  three  lengths  of  wire 
each  about  24  feet  long  and  they  could  be  con- 
nected as  one  length  or  used  as  separate  lengths. 
.  .  .  Each  was  insulated  from  the  other.  Will 
call  this  side  of  the  ring  A.  On  the  other  side,  but 
separated  by  an  interval,  was  wound  wire  in  two 
pieces,  together  amounting  to  about  60  feet  in 
length,  the  direction  being  as  with  the  former 
coils.  This  side  call  B. 

"...  Made  the  coils  on  B  side  one  coil,  and 
connected  its  extremities  by  a  copper  wire  passing 
to  a  distance  and  just  over  a  magnetic  needle, 

[59] 


Electricity:    Its  History  and  Development 

.  .  .  then  connected  the  ends  of  one  of  the  pieces 
on  A  side  with  the  battery.  Immediately  a  sensible 
effect  on  the  needle.  It  oscillated  and  settled  at 
last  in  original  position.  On  breaking  connection 
of  A  side  with  battery,  again  a  disturbance  of  the 
needle." 

Nine  years  of  thought  and  experiment,  and  then 
—  "a  sensible  effect  on  the  needle."  At  last  he  had 
the  key;  there  was  no  effect  while  the  current  was 
flowing  steadily  through  the  coil  A  —  while  the 
magnetism  of  the  core  was  constant  and  at  rest 
with  respect  to  B ;  it  was  only  when  the  magnetism 
was  changing  from  zero  to  its  normal  value  at  the 
instant  the  current  began  to  flow  through  A,  or 
changing  back  to  zero  when  the  current  through  A 
was  interrupted,  that  a  current  appeared  in  B. 
Considering  this  in  the  light  of  his  conception  of 
lines  of  magnetic  force,  what  did  a  change  in  mag- 
netism mean  to  Faraday?  What  happened  when 
the  core  was  magnetized?  Evidently  lines  of  force 
suddenly  permeated  the  core  —  that  was  the  only 
change  in  the  region  of  the  B  coil.  The  current 
appeared  at  the  instant  the  lines  linked  through  the 
coil  and  again  when  the  lines  disappeared.  Moving 
lines  of  force  then  seemed  the  necessary  condition. 

Faraday  perhaps  did  not  get  this  full  concep- 
tion until  some  years  later,  but  he  must  have  had 
it  at  least  dimly,  for  in  his  next  experiment  he  con- 
[60] 


An  Anchor  Ring  and  What  It  Held 

nected  a  coil  of  wire  wound  on  a  hollow  spool  to  his 
galvanometer  and  then  thrust  a  permanent  magnet 
into  the  opening.  Again  the  galvanometer  de- 
flected while  the  magnet  was  moving,  or  while  the 
lines  of  force  were  cutting  across  the  coiled  wire, 
the  first  throw  of  the  needle  being  in  one  or  the 
other  direction  according  as  the  magnet  moved  in 
or  out.  And  again  no  effect  was  produced  while 
the  magnet  was  stationary.  Of  course  it  was  im- 
material whether  the  magnet  or  the  coil  moved  — 
relative  motion  only  being  requisite  —  and  hence 
the  next  step  seems  obvious.  Forming  a  loop  in  a 
wire  connecting  the  ends  of  his  galvanometer  wind- 
ing, Faraday  thrust  this  quickly  between  the  poles 
of  a  very  powerful  electro-magnet  —  cut  the  lines 
with  his  conductor,  that  is  —  and  as  before  got 
unmistakable  galvanometer  deflections.  This  ex- 
periment probably  gave  him  the  inspiration  for 
constructing  a  device  which  he  called  "  a  new  elec- 
trical machine." 

A  disc  of  copper  was  mounted  as  shown  in  Fig- 
ure 6  on  a  conducting  axle  and  arranged  to  be 
turned  between  the  poles  of  a  strong  horseshoe 
permanent  magnet.  The  edge  of  the  disc  and  a 
portion  of  the  axle  were  carefully  amalgamated  and 
strips  of  lead  adjusted  to  make  sliding  contact  on 
the  amalgamated  surfaces.  As  the  disc  was  turned, 
the  successive  radii  connecting  the  axle  with  the 
[61] 


Electricity:   Its  History  and  Development 

point  of  the  edge  in  contact  with  the  outer  lead 
strip  or  brush  became  virtually  successive  wires 
moved  through  the  magnetic  field,  and  a  continuous 
flow  of  current  in  one  direction  resulted.  If  the 
direction  of  rotation  reversed,  the  current  direction 
also  reversed. 

A  new  electric  machine  indeed !  —  quite  a  differ- 
ent type  of  machine  from  the  rotating  globes,  cyl- 
inders and  discs  of  glass  which  had  previously  borne 
the  name,  for  here  was  a  true  electric  generator 
producing  —  in  a  very  small  amount  it  is  true,  but 
nevertheless,  producing  —  the  same  unidirectional 
flow  of  electricity  which  under  the  name  direct  cur- 
rent is  supplying  nearly  all  the  electric  cars  and 
many  of  the  lights  and  motors  of  this  electric  age. 
The  currents  produced  in  all  Faraday's  experiments 
by  the  relative  motion  of  lines  of  force  and  elec- 
trical conductors  he  called  induced  currents  from 
analogy  with  the  magnetism  induced  in  a  bar  of  iron 
held  near  a  magnet,  or  the  electric  charge  induced 
in  an  insulated  conductor  held  near  a  charged  body. 
Just  as  in  the  voltaic  cell  the  chemical  action  really 
produces  an  electro-motive  force,  which  can  cause  a 
current  to  flow  only  when  a  closed  circuit  is  pro- 
vided, so  in  these  induction  experiments,  the  motion 
of  the  magnetic  lines  produces  an  induced  e.  m.  f. 
in  the  conductor,  which  in  its  turn  can  cause  a  cur- 
rent only  when  some  closed  circuit  is  available. 

[62] 


Fig.  7.     Fleming's  "right  hand  rule/'  showing  the  rela- 
tion of  the  direction  of  the  E.  M.  F.  induced  in  a 
conductor  to  the  direction  of  the  motion  and 
the  direction  of  the  magnetic  field 
through  which  it  moves. 


Fig.  8.     Faraday's  rectangle  for  generating  electric  cur- 
rent from  the  earth's  magnetic  field 


An  Anchor  Ring  and  What  It  Held 

The  relation  between  the  direction  of  the  lines 
of  force  (always  taken  as  from  a  north  to  a  south 
pole  in  the  space  outside  a  magnet),  the  direction 
of  motion  of  the  conductor  relative  to  the  magnetic 
field,  and  the  direction  of  the  e.  m.  f .  induced  in  the 
conductor  can  be  deduced  from  Faraday's  observa- 
tions, but  is  best  found  in  a  given  case  by  applying 
Fleming's  "  right-hand  rule "  (see  Figure  7). 
Holding  the  thumb,  forefinger  and  middle  finger 
of  the  right  hand  so  that  each  is  at  right  angles  to 
the  other  two,  and  placing  the  hand  in  such  position 
that  the  forefinger  points  in  the  direction  of  the 
lines  of  force,  and  the  thumb  in  the  direction  of 
the  motion  of  the  conductor,  the  middle  finger  will 
point  in  the  direction  of  the  induced  e.  m.  f.,  and 
consequently,  under  closed  circuit  conditions,  in  the 
direction  of  the  current. 

Thus  in  Figure  8,  which  represents  a  rectangle 
of  wire  mounted  on  a  wooden  cross  so  that  it  can 
be  easily  rotated  about  a  horizontal  axis,  suppose 
a  north  pole  is  held  over  the  page  and  a  south  pole 
underneath,  causing  magnetic  lines  to  pass  through 
the  paper  from  above,  and  suppose  further  that  we 
slowly  turn  the  coil  on  its  axis.  The  side  of  the 
loop  shown  on  top  will  have  to  move  toward  the 
bottom  of  the  page;  and  applying  Fleming's  rule 
we  find  that  the  current  will  flow  from  left  to  right, 
while  in  the  side  of  the  loop  now  at  the  bottom 
[63] 


Electricity:   Its  History  and  Development 

which  will  be  moved  toward  the  top  of  the  page  the 
current  will  flow  from  right  to  left.  The  opposite 
direction  in  the  two  opposite  sides  means  of  course 
the  same  direction  with  reference  to  the  rectangle 
circuit,  so  that  a  unidirectional  current  flows  around 
the  loop  during  the  half -revolution,  if  the  ends  are 
joined  to  make  a  closed  circuit,  but  as  soon  as  the 
side  now  at  the  top  reaches  the  bottom  and  begins 
to  ascend,  the  current  ceases  to  flow  from  left  to 
right  and  begins  to  flow  from  right  to  left,  a  similar 
reversal  taking  place  in  the  other  side.  The  cur- 
rent, that  is,  reverses  each  time  the  rectangle  passes 
through  the  position  where  its  plane  is  at  right 
angles  to  the  lines  of  force. 

If  each  end  of  the  wire  forming  this  rectangular 
loop  were  connected  to  an  insulated  ring  mounted 
on  the  shaft,  and  two  brushes  were  arranged  to 
make  good  contact  on  these  rings  while  the  loop 
was  slowly  rotated,  a  galvanometer  connected  so 
that  its  winding  completed  the  circuit  from  brush 
to  brush,  would  show  a  current  reversing  its  direc- 
tion at  each  half -revolution  of  the  rectangle.  This 
current  would  be  a  true  alternating  current  —  the 
only  difference  between  it  and  the  alternating  cur- 
rents which  are  used  today  in  the  transmission  of 
thousands  of  horsepower  over  long  distances  being 
that  in  these  the  reversal  in  direction  takes  place 
about  50  times  each  second. 
[64] 


An  Anchor  Ring  and  What  It  Held 

Alternating  currents,  however,  appeared  quite 
useless  to  Faraday  and  his  contemporaries,  for  their 
ideas  of  current  electricity  were  based  on  the  con- 
tinuous current  from  the  voltaic  cell.  When,  there- 
fore, Faraday  made  this  rectangle  of  Figure  8  to 
demonstrate  that  his  induced  currents  could  be  pro- 
duced directly  from  the  earth's  magnetic  field  he 
found  it  necessary  to  provide  some  way  of  causing 
the  reversing  currents  in  the  loop  to  flow  in  a  single 
direction  in  the  external  circuit,  a  process  now 
generally  called  rectifying  an  alternating  current. 

For  this  purpose  he  mounted  a  cylinder  of  insu- 
lating material  on  the  shaft  concentric  with  its  axis, 
and  fitted  a  short  length  of  brass  tube  tightly  over 
this  cylinder.  He  then  connected  the  ends  of  the 
rectangle  wires  to  the  tube  at  points  opposite  one 
another  and  split  the  tube  longitudinally  along  two 
opposite  lines  midway  between  the  rectangle  sides. 
Mounting  two  brushes  as  shown,  and  rotating  the 
loop  and  split  tube,  either  brush  was  placed  in  con- 
nection with  one  or  the  other  side  of  the  rectangle 
according  as  one  or  the  other  half  of  the  tube  came 
in  contact  with  that  brush,  and  the  connection  to 
the  brushes  reversed  just  at  the  instant  the  current 
direction  reversed.  The  current  through  any  ex- 
ternal circuit  connecting  the  brushes  was  thus  con- 
tinuously in  one  direction,  and  the  loop  of  Figure 
8  could  be  used  as  an  alternating-current  or  direct- 
[65] 


Electricity:   Its  History  and  Development 

current  generator  according  as  the  coil  was 
connected  to  collector  rings  or  to  this  split  tube 
arrangement  called  a  commutator.  This  is  indeed 
the  essential  difference  between  modern  direct-cur- 
rent and  alternating-current  generators,  machines 
which  even  in  units  of  the  enormous  capacity  of 
27,000  horsepower  represent  only  the  normal  devel- 
opment of  Faraday's  wire  rectangle. 


[66J 


VI 
THE  UNITS 

IN  1801,  less  than  a  year  after  Volta  published 
his  great  discovery  of  the  pile  and  crown  of 
cups,  two  Englishmen,  Nicholson  and  Carlyle,  com- 
municated to  the  Royal  Society  their  observations 
on  the  effect  of  a  continuous  current  from  a  Voltaic 
pile  flowing  between  two  electrodes  immersed  in  a 
tube  of  river  water.  It  had  been  discovered  as 
early  as  1790  that  a  Leyden  jar  discharge  between 
metal  points  in  a  glass  of  water,  decomposed  a  small 
quantity  of  the  liquid  into  gaseous  constituents,  and 
probably  Nicholson  and  Carlyle  were  'only  trying 
to  find  another  proof  of  the  identity  of  the  two 
electricities,  "  f rictional "  and  "  voltaic,"  when  they 
began  their  experiments.  Not  only  did  they  suc- 
ceed, however,  in  producing  copious  streams  of  gas 
from  the  electrodes  as  they  had  hoped,  but  the  gases 
were  entirely  distinct,  oxygen  appearing  at  that 
electrode  at  which  the  current  entered  the  cell  and 
hydrogen  at  the  other.  In  the  Leyden  jar  experi- 
ment these  gases  were  always  mixed  together  —  a 
[67] 


Electricity:   Its  History  and  Development 

circumstance  now  well  understood  to  be  due  to  the 
fact  that  the  Ley  den  jar  discharge  consists  of  an 
electrical  oscillation,  the  current  passing  alternately 
several  times  in  either  direction  during  the  almost 
infinitesimal  interval  of  the  discharge,  but  to  the 
scientists  of  1801  the  difference  in  result  seemed  to 
indicate  a  difference  in  kind  of  electricity,  and  thus 
helped  to  delay  the  recognition  of  the  fact  that 
electricity  from  all  sources  is  identical. 

Still  they  had  found  a  most  convenient  method 
of  separating  water  into  its  components,  and  in 
1805  a  close  friend  of  Volta,  named  Brugnatelle, 
substituted  a  silver  coin  for  the  negative  electrode, 
a  solution  of  gold  for  the  water,  and  found  that  the 
electric  current  separated  this  solution  into  its  ele- 
ments and  deposited  a  firm,  even  layer  of  metallic 
gold  on  the  coin.  This  was  the  first  example  of 
electro-plating  —  the  process  used  today  in  the 
jeweler's,  engraver's  and  printer's  arts  being 
practically  identical. 

But,  as  in  almost  every  branch  of  electrical 
science  investigated  before  his  time,  it  remained  for 
Michael  Faraday  to  amplify  and  show  the  real 
meaning  of  the  discovery  of  electrolysis,  as  this  de- 
composition of  any  substance  by  an  electric  current 
is  called.  In  1834  he  became  specially  interested 
in  developing  some  method  of  accurately  measuring 
currents  or  quantities  of  electricity.  When  we 
[68] 


The  Units 

think  of  measuring  a  current  of  water  we  consider 
the  quantity  which  flows  past  a  fixed  point  in  a 
definite  time,  and  so  it  is  easiest  to  think  of  meas- 
uring a  uniform  current  of  electricity  by  finding 
the  quantity  passing  through  a  wire  in  a  second. 
Some  easily  measured  result  of  an  electric  current 
which  bears  a  fixed  relation  to  the  quantity  of  elec- 
tricity must,  then,  be  found. 

To  investigate  the  relation  between  quantity  of 
electricity  and  the  resulting  amount  of  electrolytic 
effect,  Faraday  developed  his  gas  voltameter,  con- 
sisting of  two  platinum  electrodes  immersed  in 
acidulated  water  in  a  vessel  so  arranged  that  all  the 
gas  evolved  would  collect  in  a  graduated  cylinder. 
By  a  long  series  of  experiments  he  proved  that  the 
quantity  of  gas  was  entirely  independent  of  the 
size  of  the  platinum  electrodes,  the  amount  of  acid 
which  he  added  to  the  water,  or,  indeed,  of  any 
other  condition  except  the  quantity  of  electricity 
which  passed  through  the  electrolyte.  Further- 
more, by  trying  solutions  of  various  metals  he 
found  that  the  weight  of  metal  deposited  on  the 
electrode  by  which  the  current  left  the  electrolyte 
was  in  every  case  directly  proportional  to  the  quan- 
tity of  electricity  passing.  Then  by  arranging  in 
series  a  number  of  voltameters  containing  different 
electrolytes  so  that  the  same  current  necessarily 
passed  through  each,  he  discovered  that  the  weights 
[69] 


Electricity:   Its  History  and  Development 

of  the  different  metals  deposited,  or  of  the  gases 
evolved,  bore  a  perfectly  definite  relation  to  each 
other,  which  could  be  easily  computed  from  the 
weights  of  these  substances  that  were  equivalent  in 
chemical  combining  power  to  a  given  weight  of 
hydrogen.  Here  was  the  first  proof  of  a  definite 
relation  between  chemistry  and  electricity,  a  rela- 
tion which  today  is  generally  believed  to  indicate 
an  electrical  cause  for  every  chemical  phenomenon. 

No  better  method  of  measuring  current  precisely 
is  known  than  this  voltameter  arrangement  of 
Faraday.  For  rather  complex  theoretical  reasons 
the  quantity  of  electricity  which  will  deposit  on  a 
platinum  containing-bowl,  0.001118  of  a  gram  of 
silver  from  a  certain  solution  of  silver  nitrate  has 
been  taken  as  a  unit,  and  if  this  unit  quantity  flows 
through  a  circuit  in  unit  time,  that  is,  in  one  sec- 
ond, the  electric  current  is  said  to  have  unit 
strength.  If  the  current  is  strong  enough  to  de- 
posit the  0.001118  of  a  gram  of  silver  in  one-fifth 
of  a  second,  it  is  five  times  unit  strength,  and  so  on. 
This  unit  of  current  is  named  the  ampere,  in  honor 
of  the  French  philosopher.  A  rough  conception 
of  its  magnitude  may  be  obtained  from  the  fact 
that  the  electric  current  flowing  through  an  ordi- 
nary 1 6-candlepower  incandescent  lamp  is  about  !/2 
ampere. 

With  this  method  of  accurately  measuring  elec- 
[70] 


The  Units 

trical  currents  came  the  means  of  carefully  checking 
the  law  announced  in  1827  by  George  Simon  Ohm 
to  represent  the  relation  between  the  current  pro- 
duced in  any  circuit  and  the  electro-motive  force 
or  electrical  pressure  applied  to  that  circuit.  By  a 
careful  mathematical  analysis  of  equally  careful 
experiments  Ohm  had  proved  to  his  own  satisfac- 
tion that  if  a  certain  e.  m.  f.  applied  to  a  given 
piece  of  wire  produced  a  current  value  which  we 
may  call  one  unit  of  current,  twice  the  e.  m.  f. 
would  produce  two  units  of  current;  one-half  the 
e.  m.  f .,  one-half  unit  of  current,  and  so  on ;  or,  in 
other  words,  that  for  any  definite  electrical  circuit 
the  current  has  a  constant  relation  to  the  pressure 
producing  it.  The  wire,  that  is,  appeared  to  offer 
a  constant  obstruction  to  the  flow  of  each  unit  of  cur- 
rent, and  Ohm  named  this  obstruction  the  resistance. 
Further  experiment  showed  that  the  resistance  was 
proportional  to  the  length  of  the  wire,  so  that 
with  a  constant  applied  e.  m.  f .  the  current  was 
halved  by  doubling  the  wire  length,  and  that  the 
resistance  was  also  inversely  proportional  to  the 
cross  section  of  the  wire,  or  the  current  was 
doubled  by  doubling  the  cross  section.  The  resist- 
ance of  each  substance  was  found  to  be  different, 
but  for  any  given  lot  of  one  material  the  resistance 
always  varied  as  the  length  and  inversely  as  the 
cross  section  of  the  specimen  and  was  entirely  inde- 


Electricity:   Its  History  and  Development 

pendent  of  the  amount  of  current  flowing.     Ohm 

expressed  his  law  in  the  form :  current  = '- — - — - — 

resistance 

and  although  his  contemporaries  scoffed,  and 
later  mathematicians  termed  his  methods  little  bet- 
ter than  a  guess,  this  law  stands  today  one  of  the 
simplest  and  most  perfect  statements  of  natural 
relations  known  in  any  branch  of  science. 

The  unit  of  resistance  has  been  named,  very 
appropriately,  the  ohm,  and  is  equal  to  the  resist- 
ance at  0°  Centigrade,  of  a  column  of  mercury  of 
uniform  cross  section,  106.3  centimeters  long,  and 
weighing  14*.45£1  grammes.  For  all  practical  pur- 
poses, however,  resistance  standards  are  constructed 
of  alloy  wire,  and  carefully  adjusted  to  correspond 
with  the  mercury  standards  preserved  at  the  Bureau 
of  Standards.  These  units  of  electric  current  and 
resistance  of  course  represent  the  result  of  a  vast 
amount  of  refined  research  following  the  original 
achievements  of  the  pioneers,  and  this  is  also  true 
of  the  unit  of  electrical  pressure. 

Electro-motive  force  was  first  conceived  from  the 
effect  produced  by  a  Voltaic  cell,  and  it  was,  there- 
fore, quite  natural  that  the  pressure  generated  by 
a  single  Daniels  cell  should  be  taken,  about  1840, 
as  the  first  unit  of  e.  m.  f .  Along  with  the  develop- 
ment of  the  various  forms  of  cell,  however,  many 
experimenters  had  been  working  on  the  conception 
[72] 


Standard    1-ohm   resistance  coil.      Arranged   for   immer- 
sion in  oil  bath  to  secure  constant  temperature 


Arrangement  of  iron  filings  in  plane  at  right  angles  to 
axes  of  two  parallel  conducting  wires  carrying  cur- 
rents   (a)    in   the    same,    and    (b)    in    opposite 

directions  [Page  55 


•IBk 


Standard  Weston  cell.     Adopted  as  legal  standard 
E.M.F.    January    1,    1911  [Pwc  ' 


Fig. 


Fig.  9.     Vibrator  used  in  in- 
duction coils  and  in  electric 
"J?  bells.     Lower     screw     insu- 
lated   from    circuit   portions 
10.      Siemen's    generator    with    shuttle    armature, 
E.  M.  F.  increased  by  increasing  strength  of 
magnetic  field,  turns  in  winding,  and 
speed  of  armature  revolution 


The  Units 

of  lines  of  force  suggested  by  Faraday.  In  1834 
Lenz  found  that  the  electrical  pressure  induced  in 
the  B  half  of  Faraday's  ring,  which  we  discussed  in 
the  last  chapter,  was  directly  proportional  to  the 
number  of  turns  of  wire  in  the  coil  —  that  is,  doub- 
ling the  turns  in  the  coil  doubled  the  induced  pres- 
sure. It  was  soon  found,  too,  that  the  ring  form  of 
apparatus  could  advantageously  be  replaced  by 
winding  the  A,  or  magnetizing,  coil  directly  on  a 
straight  bar  of  iron;  so  this  part  was  simply  an 
electro-magnet  over  which  the  B  coil  was  wound  as 
an  outside  cylinder  of  wire. 

This  modification  led  directly  to  the  induction 
coil,  in  which  the  current  is  interrupted  by  the 
vibrator  shown  in  Figure  9,  and  induced  e.  m.  f.'s 
are,  therefore,  generated  many  times  a  second.  As 
will  be  seen,  the  current  is  led  through  the  sta- 
tionary platinum-tipped-screw  contact  (  S  )  to  a  sim- 
ilar contact  on  a  flexible  spring  blade  (  $  )  equipped 
with  a  soft  iron  piece  (P)  opposite  the  iron  core  of 
the  coil,  thence  through  the  flexible  blade  to  the 
magnetizing  coil,  and  then  back  to  the  battery.  A 
current  flowing  magnetizes  the  core  which  attracts 
the  iron  piece  on  the  flexible  blade ;  but  as  soon  as 
this  piece  moves  toward  the  magnet  the  two  plati- 
num contacts  are  drawn  apart  and  the  circuit  is 
broken.  The  core  at 'once  loses  its  magnetism,  the 
iron  piece  flies  back,  the  circuit  is  again  made,  and 
[73] 


Electricity:   Its  History  and  Development 

the  process  is  repeated  as  many  times  each  second 
as  the  strength  of  the  spring  permits. 

In  experimenting  with  this  apparatus  it  was  soon 
observed  that  not  only  did  the  pressure  induced  in 
the  outside  or  secondary  coil  increase  with  the  num- 
ber of  turns  in  that  coil,  as  Lenz  had  found,  but  it 
also  increased  with  the  number  of  times  the  mag- 
netizing current  was  interrupted  each  second. 
Interpreting  these  and  other  facts  in  the  light  of 
Faraday's  theory,  Neumann  in  1845  discovered  the 
law  that  the  pressure  induced  in  any  wire  depends 
only  on  the  rate  at  which  magnetic  lines  cut  it,  or, 
in  other  words,  on  the  number  of  lines  of  magnetic 
force  crossing  the  wire  each  second.  In  the  induc- 
tion coil  —  since  all  the  lines  of  force  threading  the 
core  form  closed  loops  extending  from  one  end  of 
the  core  to  the  other  in  the  space  outside  —  practi- 
cally all  these  loops,  all  these  lines  of  force,  cut 
each  turn  of  the  secondary  winding  whenever  the 
circuit  is  made  and  again  when  it  is  broken,  and 
adding  to  the  number  of  turns  cut  by  a  given  num- 
ber of  lines  is  strictly  equivalent  to  adding  to  the 
number  of  lines  cutting  one  turn.  Similarly, 
increasing  the  interruptions  of  the  magnetizing  or 
primary  current,  and  thereby  increasing  the  num- 
ber of  times  per  second  which  these  lines  cut  the 
turns,  is  just  the  same  as  increasing  the  number 
of  lines  cutting  the  turns  once  each  second. 

[74] 


The  Units 

In  1856  Werner  Siemens  applied  these  principles 
to  the  construction  of  the  electric  generator  shown 
in  Figure  10,  in  which  a  strong  magnetic  field  is 
supplied  by  a  group  of  permanent  magnets  of 
horseshoe  form,  and  an  iron  core  of  shuttle-shaped 
cross-section  is  arranged  to  be  rotated  rapidly,  by 
belted  pullej^s,  in  a  circular  opening  between  the 
magnet  poles.  Instead  of  a  single  turn  of  wire  as 
in  Faraday's  rectangle,  the  core  is  wound  with 
many  turns,  and  thus  the  pressure,  directly 
dependent  on  the  number  of  lines  cut  per  second, 
is  greatly  increased. 

These  various  developments  gradually  changed 
the  fundamental  idea  of  electric  pressure  from  that 
of  a  condition  generated  in  a  battery  to  that  of  the 
effect  produced  in  a  wire  cutting  lines  of  force,  and 
so  today  we  find  the  scientific  definition  of  the  unit 
of  e.  m.  f .  to  be  "  the  pressure  produced  in  a  wire 
cutting  lines  of  magnetic  force  at  the  rate  of  100,- 
000,000  per  second."  This  pressure  is  called  one 
volt,  in  honor  of  Volta,  and  is  very  nearly  that  of 
the  Daniels  cell  originally  taken  as  the  standard. 
The  legal  definition,  however,  is  still  given  in  terms 
of  a  battery,  being  derived  from  the  statement  that 
a  certain  cell  invented  by  Dr.  Weston,  of  Newark, 
N.  J.,  has  an  e.  m.  f.  of  1.08183  volts.  Methods  of 
measurement  have  been  devised  whereby  the  pres- 
sure of  this  cell  is  used  as  a  standard,  although 
[75] 


Electricity:   Its  History  and  Development 

practically  no  current  is  taken  from  it,  and  under 
these  conditions  the  cell  voltage  will  remain  con- 
stant over  long  periods  of  years. 

The  volt,  the  ampere,  and  the  ohm  have  been 
so  chosen  that  if  the  electrical  quantities  in  any 
circuit  are  expressed  in  these  units,  Ohm's  law  is 
found  to  be  fulfilled;  that  is,  one  volt  pressure 
applied  to  the  ends  of  a  one-ohm  resistance  will 
cause  one  ampere  to  flow,  or  the  current  in  amperes 
equals  the  pressure  in  volts  divided  by  the  resistance 
in  ohms. 


[76] 


VII 
THE  SYMPATHETIC  NEEDLE 

THE  application  of  magnetism  or  electricity  to 
the  transmission  of  some  form  of  signals 
readily  translated  into  words,  seems  to  have  been 
a  favorite  dream  of  even  the  earliest  electrical 
philosophers.  In  the  sixteenth  century  John  Porta 
described,  in  apparent  good  faith,  a  "  sympathetic  " 
magnetic  needle  mounted  to  swing  over  a  circular 
table  about  the  circumference  of  which  the  alphabet 
was  written  —  this  needle  causing  another,  mag- 
netized from  the  same  lodestone  and  similarly 
mounted,  to  move  in  perfect  accord  no  matter  how 
great  the  distance  separating  the  two !  If,  then, 
the  first  was  swung  to  point  to  any  letter  the  second 
at  once  indicated  the  same  letter,  and  thus,  accord- 
ing to  Porta,  "  To  a  friend  at  a  distance  shut  up 
in  prison  we  may  relate  our  minds." 

This  telegraph,  of  course,  like  most  of  the  scien- 
tific discoveries  of  the  sixteenth  century  meta- 
physicians, was  purely  imaginary,  and  with  our 
present  knowledge  of  the  limited  space  through 
which  even  the  strongest  artificial  magnet  produces 
[77] 


Electricity:   Its  History  and  Development 

an  appreciable  magnetic  field,  the  idea  seems  per- 
haps absurd;  but,  after  all,  it  is  not  such  a  very 
different  conception  from  that  which  has  resulted 
in  wireless  telegraphy;  and,  without  experimental 
verification,  Porta's  assertion  is  quite  as  credible  as 
Marconi's.  It  served  at  least  to  direct  the  thought 
of  electricians  to  the  transmission  of  intelligence, 
and  as  each  one  of  the  great  electrical  phenomena 
was  discovered,  it  was  sure  to  be  scrutinized  by 
some  one  for  adaptability  to  this  service. 

In  1753  a  scheme  was  proposed  for  employing 
frictional  electricity,  in  which  twenty-six  wires  cor- 
responding to  the  alphabet  were  to  be  strung  on 
insulators  from  the  sending  to  the  receiving  sta- 
tion, where  each  wire  was  to  be  equipped  with  a  pair 
of  pith  balls  suspended  by  linen  threads.  An  elec- 
tric charge  imparted  to  any  wire  at  the  sending 
station  would  distribute  itself  along  that  wire  and 
electrify  the  pith  balls,  causing  them  to  diverge. 
This  method  was  very  slow,  but  with  some  slight 
improvements  it  was  installed  by  Le  Sage  at  Geneva 
in  1774«,  and  thus  ranks  as  the  first  working  electric 
telegraph.  The  twenty-six  wires  proved  difficult  to 
maintain ;  and  in  a  few  years  Lomond  devised  a  sys- 
tem of  signals,  using  a  single  wire  with  a  sensitive 
pair  of  pith  balls  at  each  end  of  the  line,  the  vari- 
ous letters  being  indicated  by  different  numbers  and 
magnitudes  of  divergencies. 
[78] 


The  Sympathetic  Needle 

The  Voltaic  cell  suggested  new  possibilities.  In 
1812  Soemmering  returned  to  the  twenty-six  wire 
scheme,  his  wires  ending  in  26  gold  needles 
immersed  in  a  trough  of  acidulated  water;  and 
the  signal  being  sent  by  connecting  a  battery  to 
any  two  wires,  when  the  gases  liberated  by  elec- 
trolysis in  the  trough  indicated  the  two  letters 
chosen,  the  order  of  the  letters  being  determined  by 
always  reading  first  the  needle  liberating  hydrogen. 
Ampere  in  his  first  work  on  Oersted's  discovery 
described  a  telegraph  to  use  twenty-six  magnetic 
needles  deflected  by  current  sent  over  twenty- 
six  circuits;  and  Gauss  and  Weber  in  1833 
improved  this  scheme  by  substituting  a  single  heavy 
needle  for  Ampere's  twenty-six,  and  a  Faraday 
induced-current  generator,  consisting  of  a  coil  to 
be  thrust  over  a  bar  magnet,  for  the  unreliable 
Voltaic  cells  available  at  thejbime.  This  apparatus 
was  actually  installed  at  Gottingen ;  t  and  it  was 
while  experimenting  on  improvements  in  the  Gauss 
and  Weber  arrangement  that  Steinheil  discovered, 
in  1837,  that  the  earth  could  be  used  for  the  return 
circuit  and  that  only  one  wire,  therefore,  was  neces- 
sary. 

The  resistance  between  opposite  faces  of  a  cubic 

inch  of  earth  is  many  times  greater  than  for  a  cube 

of  metal,  and  at  first  sight  it  might  appear  that  the 

earth  return  would  have  such  a  high  resistance  as  to 

[79] 


Electricity:   Its  History  and  Development 

make  it  impracticable  to  send  through  it  sufficient 
currents  for  long  distance  telegraphy.  As  we  saw  in 
the  last  chapter,  however,  the  resistance  of  a  con- 
ductor is  inversely  proportional  to  its  area  and 
while  the  area  of  a  wire  is  strictly  limited  by  the 
cost  of  the  wire  itself  and  of  the  supports  necessary 
to  secure  it  properly,  the  area  of  the  earth  circuit 
is  almost  unlimited,  and  its  resistance  is  thus  found 
to  be  negligible  if  a  sufficiently  good  connection  is 
made  by  burying  large  plates  of  copper  in  moist 
ground. 

But  although  the  German  pioneers  were  thus 
making  genuine  advances,  the  first  really  successful 
development  of  Ampere's  idea  was  made  in  Eng- 
land by  Cooke  and  Wheatstone,  who  in  1837  pat- 
ented the  five-needle  telegraph  shown  in  Figure  11. 
Six  wires  were  used  in  this  system,  and  the  needles 
were  so  deflected  in  pairs  by  sending  a  current 
through  coils  lying  between  them  that  the  desired 
letter  was  found  on  the  backboard  above  or  below 
the  needles  at  the  spot  to  which  the  pair  pointed. 
The  control  of  these  double  deflections  required  the 
manipulation  of  ten  switches  or  keys  for  opening 
and  closing  the  various  circuits. 

Almost  simultaneously  with  the  patenting  of  this 
system,  Professor  Daniels  announced  his  voltaic 
cell,  which  in  the  form  of  the  Gravity  battery  com- 
pletely filled  the  demand  for  a  long-lived  source  of 
[80] 


The  Sympathetic  Needle 

constant  electric-motive  force.  All  the  requisites 
for  a  commercially  successful  telegraph  were  thus 
at  last  available,  and  soon  the  5-needle  instruments 
were  working  in  various  parts  of  England. 

In  America,  however,  development  had  proceeded 
along  quite  a  different  line.  Joseph  Henry,  work- 
ing in  his  high-school  laboratory,  during  the  scant 
leisure  of  a  teacher,  had  constructed  electro-mag- 
nets of  various  forms  and  sizes  until  he  had  found 
that  a  magnet  at  the  end  of  a  long  line  of  con- 
necting wire,  if  wound  with  many  turns  and  sup- 
plied by  several  cells  of  battery  in  series,  had  as 
great  strength  as  the  magnets  previously  made 
with  a  few  turns  and  connected  directly  to  one  or 
two  cells  of  battery.  In  modern  terms  this  means 
that,  according  to  Ohm's  law,  if  the  resistance  of 
the  circuit  is  increased  by  adding  to  the  length  of 
line,  the  e.  m.  f.  must  also  be  increased  to  maintain 
the  same  current ;  and  that  as  the  resistance 
increases  beyond  our  ability  to  maintain  the  cur- 
rent with  any  reasonable  e.  m.  f.,  and  the  current 
strength  is,  therefore,  allowed  to  decrease,  the 
strength  of  the  magnet  may  be  maintained  by  car- 
rying the  weaker  current  more  times  around  the 
core.  But  although  these  laws  had  already  been 
stated,  few  seem  to  have  appreciated  their  signifi- 
cance and  Henry's  discoveries  were  discussed  in  the 
form  first  given.  The  electro-magnet  then,  if  prop- 
[81] 


Electricity:   Its  History  and  Development 

erly  designed,  could  be  energized  from  a  battery  at 
a  distance  —  the  application  to  telegraphy  was 
obvious. 

Some  time  about  1832  Samuel  B.  Morse,  who  two 
years  before  had  seen  in  Henry's  lecture  hall  an 
electro-magnet  arranged  to  give  audible  signals 
and  controlled  through  wires  carried  several  times 
around  the  room,  began  to  work  on  a  scheme  for 
making  the  magnet  record  the  signals.  After  much 
hardship  he  produced,  and  exhibited  publicly  in 
1837,  the  first  recording  telegraph  instrument, 
shown  in  Figure  12.  As  will  be  seen,  the  battery 
circuit  was  closed  when  the  metal  arm  on  the 
end  of  the  lever  L  dipped  into  the  mercury  cups  at 
V,  the  motion  of  the  lever  being  produced  by  run- 
ning under  the  projection  at  N  a  rule  in  which 
"type,"  similar  to  those  shown  at  1  and  3,  were 
set,  each  point  on  a  type  tilting  the  lever  and  pro- 
ducing a  momentary  contact  in  the  mercury.  The 
electro-magnet  at  E  was  arranged  to  attract  a  piece 
of  iron,  called  an  armature,  fixed  to  the  light 
swinging  frame  OB,  which  carried  at  B  a  pencil  for 
marking  a  zigzag  line  on  the  moving  strip  of  paper 
r,  the  shape  of  the  line  corresponding  to  the  par- 
ticular combination  of  "type"  used.  Morse 
claimed  as  his  invention,  the  metal  type  signifying 
numbers,  the  recording  mechanism,  a  code  by  which 
all  common  words  were  given  representative  nun> 
[82] 


Fig.  11.  Cooke  and 
Wheatstone's  original 
five-needle  telegraph 
which  has  been  modi- 
fied into  the  single- 
needle  instrument  still 
used  in  England. 

[Page  80 


Fig.    12.      The   first 
Morse  telegraph 

[Page  82 


The  Sympathetic  Needle 

bers,  and  a  scheme  for  laying  the  wires  under- 
ground in  tubes  —  none  of  which  are  used  in  thue 
so-called  Morse  system  of  today. 

By  1843  Morse  had  gained  sufficient  influence  to 
secure  an  appropriation  of  $30,000  from  the 
United  States  Government  for  building  an  experi- 
mental line  from  Baltimore  to  Washington;  this 
was  completed,  and  the  first  message  sent  in  May, 
1844.  In  this  line  Steinheil's  earth  return  circuit 
was  used,  and  the  line  wire  was  at  first  carried 
underground;  but  the  underground  construction 
proved  so  expensive  to  maintain  that  the  line  was 
soon  changed  to  an  overhead  wire  on  poles.  The 
underground  wire  was  the  last  of  Morse's  ideas  to 
be  abandoned.  His  partner,  Alfred  Vail,  had  sub- 
stituted for  the  zigzag  line  recorder  an  apparatus 
in  which  the  electro-magnet  merely  pressed  a  pen 
against  the  moving  strip  of  paper  for  longer  or 
shorter  intervals,  and  this  made  a  series  <of  long  and 
short  marks,  called  respectively  dashes  and  dots, 
separated  by  spaces.  These  marks  represented 
directly  letters  of  the  alphabet  and  so  spelled  the 
words  of  the  message  without  the  cumbersome  inter- 
mediate code  of  numbers;  and  the  "type"  and 
lever  were  replaced  by  a  simple  key,  which  closed 
the  circuit  when  depressed  by  hand. 

One  essential  to  success,  however,  Morse  had 
foreseen  and  provided.  "  Suppose,"  he  wrote, 
[83] 


Electricity:   Its  History  and  Development 

"  that  in  experimenting  on  twenty  miles  of  wire  we 
should  find  that  the  power  of  magnetism  is  so  feeble 
that  it  will  move  a  lever  with  certainty  but  a  hair's 
breadth;  that  would  be  insufficient,  it  may  be,  to 
write  or  print,  yet  it  would  be  sufficient  to  close  and 
break  another  or  a  second  circuit  twenty  miles  far- 
ther; and  this  circuit  could  in  the  same  manner  be 
made  to  break  and  close  a  third  circuit  twenty  miles 
farther;  and  so  on,  around  the  globe."  Here  was 
the  principle  of  the  device  which  has  since  come  to 
be  called  the  relay,  and  which  is  now  part  of  every 
telegraph  station.  For  it  was  soon  found  that  the 
more  skillful  operators  of  the  original  instruments 
read  the  messages  from  the  clicks  which  the  pen 
arm  of  the  receiver  made  when  pulled  against  the 
tape  and  when  released  —  a  considerable  interval 
between  clicks  corresponding  to  a  dash,  a  shorter 
interval  to  a  dot.  But  at  the  best  the  clicks  were 
very  faint  and  required  strained  attention.  Why 
not  apply  the  relay  as  suggested  by  Morse  to  con- 
trol a  local  battery  in  the  receiving  station,  which, 
however,  instead  of  sending  the  signal  forward  to 
another  station  should  energize  a  powerful  electro- 
magnet to  be  called  a  sounder,  making  clicks  loud 
enough  to  be  easily  heard?  This  system  has  proved 
so  much  more  rapid  than  the  recording  apparatus, 
especially  since  the  typewriter  has  come  into  use 
for  taking  the  message,  that  tape  recorders  are  now 
[84] 


The  Sympathetic  Needle 

rarely  seen  except  in  such  special  applications  as 
stock  "  tickers." 

The  most  usual  arrangement  of  the  modern  tele- 
graphic circuit  is  shown  in  Figure  13.  When  the 
line  is  not  in  use  the  switches  Sw  are  closed  at  all 
stations,  and  current  from  the  main  battery  B  flows 
through  the  line  and  relay  coils  in  series,  and  back 
through  the  earth.  The  relays  R  are  thus  mag- 
netized and  attract  their  armatures,  closing  the 
various  local  circuits  and  so  energizing  the  sounder 
magnets  S,  which  in  turn  draw  their  armatures 
against  the  lower  stop.  If  now  the  operator  at  the 
left  hand  station  wishes  to  send  a  dispatch,  he  opens 
switch  Sw,  breaking  the  circuit;  the  relays,  and 
through  them  the  sounders,  are  demagnetized,  the 
sounder  armatures  fly  up  against  the  upper  stop 
under  the  action  of  the  control  springs,  and  the 
operator  by  manipulating  the  key  K  closes  and 
opens  the  circuit  at  will,  a  click  in  his,  own  sounder 
and  in  that  of  each  sounder  along  the  line  being 
heard  at  each  make,  and  a  slightly  different  click  at 
each  break.  The  line  may  theoretically  be  extended 
to  include  as  many  stations  as  desired  by  simply 
taking  the  wire  from  the  key  of  the  second  station 
to  the  relay  of  a  third,  instead  of  to  earth,  and  so 
on ;  but  twenty-five  stations  in  series  have  been 
found  to  give  as  much  business  as  it  is  practical  to 
handle  over  one  wire. 

[85] 


Electricity:   Its  History  and  Development 

Many  complications  have  been  added  to  this  sys- 
tem to  meet  special  needs.  Several  ways  of  sending 
two  simultaneous  messages  over  the  same  line,  one 
in  either  direction,  were  devised  before  1860. 
Thomas  A.  Edison  made  his  first  appearance  as  a 
notable  pioneer  in  1873  with  an  entirely  successful 
method  for  sending  two  simultaneous  messages  in 
the  same  direction  over  a  single  wire.  Edison  and 
others  have  devised  apparatus  for  sending  over  any 
line  four  simultaneous  messages  —  two  in  either 
direction  —  and  all  these  systems  are  in  daily  use  on 
important  lines.  But  the  germ  of  all  —  the  real 
pioneer  electro-magnetic  telegraph  —  was  installed 
over  eighty  years  ago  to  demonstrate  to  the  high- 
school  boys  of  Albany  the  curious  facts  which 
Joseph  Henry  had  discovered  during  the  summer 
vacation.  Understanding  these  facts,  the  telegraph 
systems  of  the  world  seem  but  an  inevitable 
development. 


[86] 


r 


Sw 


LP- 


I |I|I|I|I|I|I|I|I|IH 

i        B  i 

Fig.    13.     The  simple  telegraph  circuit 
^^~ WATCH  SPRING 


oooo 


"X 


MOTION 


t 

VAT  RE.ST 


>EC-        TIME.  *• 

Fig.    14.      Bell's   vibrating  multiplex   telegraph   and   its 
effect  on  line  current  [Page  90 


MELMBRANE. 


5PEAK 


Fig.  15.     The  Bell  telephone  as  described  in  the  original 
patent  [Page  92 


LINE: 


Fig.    16.      Bell's    magneto    electric    telephone,   the    first 
entirely  successful  telephone  instrument 

[Page  P2 


VIII 
FROM  TELEGRAPH  TO  TELEPHONE 

GIVEN,  the  Morse  Sounder  with  its  armature 
vibrating  slowly  in  response  to  signaling 
currents,  controlled  by  the  vibrations  or  movements 
of  a  sending  key ;  and  the  increasing  appreciation 
of  the  fact  that  all  sounds  were  produced  by  vibra- 
tions of  the  sounding  body,  were  transmitted  by 
vibrations  of  the  air,  and  were  heard  by  vibrations 
of  the  ear  drum;  and  it  was  almost  inevitable  that 
some  one  should  sooner  or  later  conceive  the  idea 
of  making  the  key  vibrate  at  the  same  rate  as  the 
air  particles  transmitting  a  sound,  and  thus  through 
the  action  of  the  sounder  armature  start  a  new 
series  of  air  vibrations  at  a  distant  point,  or,  in 
effect,  transmit  the  sound  by  means  of  the  tele- 
graphic circuit. 

As  early  as  1854  a  Frenchman  named  Charles 
Bourceul  saw  the  possibility  of  this  application, 
and  wrote :  "  Suppose  a  man  speaks  near  a  mov- 
able disc  sufficiently  flexible  to  lose  none  of  the  vibra- 
tions of  the  voice,  and  that  this  device  alternately 
makes  and  breaks  the  current  from  a  battery ;  you 
[87] 


Electricity:   Its  History  and  Development 

may  have  at  a  distance  another  disc  which  will 
simultaneously  execute  the  same  vibrations."  But 
Bourceul  was  content  with  stating  his  idea,  and 
apparently  made  no  attempt  to  construct  an 
apparatus  which  should  realize  it. 

Such  an  apparatus  was  constructed  by  Johann 
Philipp  Reis,  with  beer  barrel  bungs,  sausage  skin, 
and  bits  of  brass  as  materials,  and  in  1861  brought 
to  such  a  state  of  completion  that  a  description  was 
published.  In  the  original  device  a  bit  of  metal 
was  attached  to  the  center  of  a  membrane  tightly 
stretched  over  a  circular  opening  in  a  wooden 
frame,  and  a  contact  spring  arranged  to  touch  the 
metal  centerpiece  very  lightly.  An  electrical  cir- 
cuit was  connected  to  include  the  contact  between 
the  spring  and  centerpiece,  and  led  through  a  bat- 
tery and  a  light  electro-magnet  having  a  steel 
knitting  needle  for  a  core,  mounted  on  a  sounding 
box.  This  electro-magnet  receiver  was  an  idea  of 
Reis's,  based  on  the  discovery  of  Professor  Page, 
of  Salem,  Massachusetts,  who  had  found  that  a  dis- 
tinct click,  probably  due  to  the  rearrangement  of 
the  molecules,  could  be  heard  in  the  core  of  an 
electro-magnet  suddenly  magnetized  or  demag- 
netized. If  then  a  musical  note  was  sounded  near 
the  Reis  transmitter  the  membrane  was  thrown  into 
vibration,  and  the  light  contact  of  the  metal  center 
against  the  spring  was  broken  as  many  times  each 
[88] 


From  Telegraph  to  Telephone 

second  as  corresponded  to  the  particular  note,  and 
in  consequence  a  series  of  clicks  of  the  same  fre- 
quency, or  in  other  words,  a  sound  of  the  same 
pitch,  issued  from  the  receiver. 

Unfortunately,  it  was  only  a  note  of  the  same 
pitch  and  did  not  necessarily  resemble  the  sound  to 
be  transmitted  any  more  nearly  than  a  note  from  a 
tin  whistle  resembles  the  same  note  from  a  violin. 
This  failure  to  transmit  the  quality  of  the  sound 
proved  fatal  when  it  was  attempted  to  use  the  Reis 
telephone,  as  he  named  his  apparatus,  for  the  trans- 
mission of  speech.  Even  the  natural  prejudice  of 
the  inventor  only  produced  the  claim  that  "  if  you 
will  come  and  see  me  here,  I  will  show  you  that 
words  also  can  be  made  out."  The  making  out  of 
an  occasional  word  was  not  sufficiently  practical  to 
attract  the  attention  of  the  world;  Reis  had  only 
the  meager  resources  of  a  poor  German  teacher, 
and  thus  his  work  was  neglected  and,  almost  for- 
gotten. 

But  the  vision  of  Bourceul  was  still  to  be  realized, 
although  not  quite  in  the  way  he  outlined.  In  1876 
at  the  Centennial  Exhibition  at  Philadelphia  was 
shown  a  device  having  Bourceul's  two  discs  vibrat- 
ing simultaneously  —  a  successful  speaking  tele- 
phone, the  irivention  of  Alexander  Graham  Bell. 
Professor  Bell  was  unusually  well  prepared  for 
telephone  invention,  as  much  of  his  life  had  been 
[89] 


Electricity:   Its  History  and  Development 

spent  in  study  of  the  laws  of  sound  and  of  the 
voice,  required  by  his  work  in  teaching  deaf  mutes 
to  speak.  Early  in  the  seventies  he  had  been  inter- 
ested in  telegraphy  and  had  devoted  himself  to 
developing  a  system  for  sending  any  number  of 
messages  simultaneously  over  the  same  wire. 

One  scheme  which  he  had  devised  for  this  multi- 
plex telegraphy  is  shown  in  Figure  14.  Here  a 
continuous  current  flows  through  the  sending  and 
receiving  magnets  energizing  or  magnetizing  the 
cores,  and  a  series  of  watch  springs  (one  pair  only 
is  shown)  having  different  frequencies  of  vibration 
are  mounted  over  the  cores.  With  the  springs  at 
rest  a  steady  current  which  may  be  indicated  by 
the  uniform  height  of  the  straight  line  marked  "  at 
rest,"  in  the  lower  part  of  the  figure,  flows  through 
the  circuit.  If  now  one  of  the  springs  over  the 
sending  magnet  is  "  plucked  "  and  thus  thrown  into 
vibration  as  it  approaches  the  magnet  core  more 
magnetic  lines  pass  through  the  magnetic  circuit; 
while  as  it  recedes  from  the  core  the  number  of 
magnetic  lines  decreases;  and  this  movement  of 
lines  of  force  across  the  winding  of  the  magnet 
causes  an  alternating  e.  m.  f .  to  be  generated  in 
the  coil  which  periodically  aids  and  opposes  the 
e.  m.  f.  of  the  battery  in  the  circuit.  As  a  result 
the  current  through  both  the  sending  and  receiving 
magnets  is  now  represented  by  the  height  of  the 
[90] 


From  Telegraph  to  Telephone 

wavy  line  in  the  lower  figure  —  which  simply  means 
that  the  current  varies  with  the  passage  of  time 
as  the  height  of  the  wavy  line  varies  when  we  pass 
from  left  to  right  of  the  figure.  In  other  words, 
the  receiving  magnet  is  strengthened  and  weak- 
ened as  many  times  per  second  as  the  sending  spring 
vibrates,  and  in  consequence  that  receiving  spring 
which  has  the  same  natural  frequency  —  or  would 
vibrate  the  same  number  of  times  per  second  if 
plucked  —  is  thrown  into  violent  vibration. 

Bell's  training  in  acoustics  enabled  him  at  once 
to  appreciate  that  this  method  of  transmitting 
vibrations  might  be  so  modified  as  to  succeed  where 
the  make  and  break  method  failed  —  that  is,  in  the 
transmission  of  "quality"  of  sound.  For  quality 
depends  not  on  the  frequency  of  the  vibrations  con- 
stituting the  main  tone  but  upon  the  lesser  vibra- 
tions of  higher  frequencies  superimposed  upon  this 
tone,  so  that  while  two  voices  sounding  the  note  A 
would  each  produce  427  main  vibrations  per  sec- 
ond, one  might  also  produce  simultaneously  lesser 
vibrations  of  frequencies  520,  710,  and  900;  while 
the  other  might  produce  frequencies  of  610,  780, 
and  840,  resulting  in  entirely  different  qualities  of 
tone.  The  make  and  break  transmitter  would  tend 
to  transmit  only  the  main  note,  for  it  could  vibrate 
at  only  one  frequency  at  a  time,  but  if  the  watch 
spring  of  Figure  14  were  replaced  with  an  elastic 
[91] 


Electricity:    Its  History  and  Development 

diaphragm,  Bell  believed  this  diaphragm  would 
vibrate  simultaneously  at  all  the  frequencies 
required  by  voice  quality. 

Accordingly  in  his  application  for  a  patent  on 
his  cumbrous  multiplex  telegraph  he  included  a 
claim  covering  the  telephone  shown  in  Figure  15, 
in  which,  for  the  watch  springs,  are  substituted 
small  soft  iron  armatures  attached  to  membranes 
stretched  over  the  openings  of  truncated  cones 
appropriate  for  hearing  and  speaking.  This  form 
of  telephone  was  constructed  later  and  tried  out  in 
the  course  of  the  prolonged  litigation  over  the  Bell 
patents,  and  although  very  imperfect  in  compari- 
son with  our  present  instruments  it  could  be  made 
to  transmit  speech. 

The  "  Centennial "  telephone  contained  many 
improvements  on  Bell's  original  patent,  but  the 
first  entirely  successful  Bell  telephone  was  that 
covered  by  his  second  patent  and  shown  in  Figure 
16.  In  this  instrument  he  replaced  the  moisture 
absorbing  membrane  by  a  disc  of  thin  "  ferrotype  " 
iron,  and  eliminated  the  necessity  for  a  battery  by 
magnetizing  the  soft-iron  cores  of  his  electro-mag- 
nets through  direct  contact  with  permanent  bar 
magnets.  He  also  greatly  improved  the  distinct- 
ness of  transmission  by  including  a  shallow  air 
chamber  between  the  diaphragm  and  the  hearing 
orifice  —  all  features  retained  in  the  receivers  used 
[92] 


From  Telegraph  to  Telephone 

today  which,  indeed,  are  practically  the  same  as 
these  early  Bell  instruments. 

In  the  figure  the  circuit  is  shown  with  the  same 
earth  return  arrangement  as  is  used  in  telegraphy, 
and  most  of  the  early  telephones  were  so  installed. 
But  the  telephone  receiver  is  so  much  more  sensitive 
than  the  telegraph  relay,  being  affected  by  even  one 
millionth  of  the  current  through  an  ordinary  16 
candle-power  incandescent  lamp,  that  stray  cur- 
rents flowing  through  the  earth  from  telegraph 
lines  and  from  electric  railway  and  other  power 
circuits  frequently  produced  such  deafening  noises 
that  the  ground  return  had  to  be  abandoned  an<: 
all-wire  circuits  used. 

It  was  soon  found,  too,  that  whereas  the  mag 
neto  telephone  was  sensitive  to  almost  infinitesimal 
currents  when  used  as  a  receiver  it  unfortunately 
produced  e.  m.  f.'s  of  equally  infinitesimal  magni- 
tude when  used  as  a  transmitter,  and  that  in  con- 
sequence even  the  extreme  delicacy  of  the  receiver 
was  insufficient  to  respond  when  the  line  length, 
and  therefore  the  resistance  of  the  circuit,  became 
considerable,  reducing  the  current  in  accordance 
with  Ohm's  law.  Evidently,  then,  if  long  distance 
telephony  were  to  become  practical  some  means  of 
producing  stronger  currents  must  be  devised. 

Almost  before  the  demand  was  formulated,  the 
microphone,  the  device  which  was  to  satisfy  it,  was 
[93] 


Electricity:   Its  History  and  Development 

discovered  by  Professor  Hughes,  and  independently 
rediscovered  by  Edison  in  1878.  One  form  of 
Hughes's  apparatus  is  shown  in  Figure  17,  and 
consists  simply  of  two  pointed  blocks  of  carbon 
held  lightly  in  contact  by  clamping-springs  and 
mounted  on  a  sounding  board.  If  an  electric  cir- 
cuit is  taken  through  the  carbon  contact  and  thence 
through  a  battery  and  Bell  receiver,  any  sound 
throwing  the  sounding  board  into  vibration  is 
loudly  repeated  in  the  receiver  provided  that  the 
carbons  are  so  adjusted  that  contact  between  them 
is  never  broken.  This  peculiar  action  of  the  car- 
bon microphone  contact  is  not  yet  entirely  under- 
stood, but  is  believed  to  be  due  to  the  variation  in 
the  number  of  particles  in  contact  as  the  carbons 
are  pressed  more  or  less  closely  together  by  the 
vibrations  —  more  contacts  giving  more  paths  for 
the  current  or  less  resistance,  fewer  contacts  giving 
fewer  paths  or  greater  resistance.  The  same  effect 
can  be  obtained  less  perfectly  with  metal  contacts, 
and  it  is  probable  that  the  words  actually  trans- 
mitted by  Reis's  telephone  got  through  his  metallic 
contact  by  this  microphone  action  when  adjustment 
was  such  as  to  prevent  the  vibrations  causing  makes 
and  breaks. 

At    first,    however,    both    Hughes    and    Edison 
believed  the  microphone  action  to  be  due  to  changes 
in  the  resistance  of  the  body  of  the  carbon,  cor- 
[94] 


Fig.  17.      The  Hughes    microphone  on 

which  the  present  standard  transmitter 

is  based 


Fig.   18.       An    early    form  of    Edison 
carbon  transmitter 


7>  5 


Fig.    19.      Edison's   application  of  the  induction  coil  to 
long  distance  telephony  [Page  96 


From  Telegraph  to  Telephone 

responding  to  changes  in  the  pressure,  rather  than 
in  changes  of  the  contact  resistance ;  and  acting  on 
this  theory,  Edison  constructed  several  forms  of 
microphone  transmitters.  One  of  these  is  shown 
in  Figure  18.  In  this  apparatus  the  carbon  block 
C  is  placed  between  a  fixed  metal  back  plate  and  a 
thin  movable  platinum  plate  P  —  these  two  plates 
forming  the  connection  between  the  circuit  and  the 
carbon.  The  vibrations  of  the  diaphragm  are 
transmitted  through  the  metal  button  A  and  glass 
plate  G,  and  serve  to  vary  the  pressure  upon  C, 
or,  according  to  the  later  theory,  the  number  of 
contacts  between  C  and  the  two  plates.  This  trans- 
mitter and  others  constructed  on  similar  lines 
proved  to  be  capable  of  controlling  much  stronger 
fluctuating  currents  than  could  be  generated  in  the 
simple  Bell  instrument.  True,  it  was  necessary  to 
use  a  battery  for  the  source  of  e.  m.  f.  as  in  the 
original  telephones,  but  with  the  carbon  trans- 
mitter, increase  in  the  number  of  cells  resulted 
directly  in  increased  distance  of  transmission;  the 
battery,  therefore,  became  an  active  element  in  the 
development. 

As  the  view  that  the  microphone  action  was  due 
to  contact  resistance  gained  acceptance,  the  solid 
carbons  of  the  new  forms  of  transmitter  were  grad- 
ually replaced  by  various  forms  of  small  boxes  or 
cells  containing  granular  or  powdered  carbon  — 

[95] 


Electricity:   Its  History  and  Development 

each  grain  of  carbon  becoming  one  element  in  a 
tiny  microphone  and  the  number  of  contacts  being 
thus  indefinitely  increased.  Considerable  difficulty 
was  experienced  at  first  from  the  tendency  of  the 
carbon  granules  to  jam  together  or  pack,  but  this 
has  been  practically  overcome  in  various  ways  such 
as  the  introduction  in  the  containing  cell  of  per- 
forated partitions,  and  today  the  granular  carbon 
transmitter  is  the  standard  equipment  for  all  long- 
distance telephones. 

The  success  of  these  long-distance  lines,  however, 
depends  largely  on  a  third  element  introduced  by 
Edison.  For  as  the  resistance  of  the  line  becomes 
considerable,  even  the  rather  wide  variations  in 
the  resistance  of  the  granular  transmitter  under 
vibration  is  a  very  small  proportional  variation  in 
the  total  circuit  resistance,  and  in  consequence  the 
fluctuations  in  the  current  are  an  equally  small  per- 
centage of  the  current  flowing  through  the  receiver. 
To  meet  these  conditions  Edison  arranged  the  con- 
nection shown  in  Figure  19,  in  which  the  transmitter 
T  is  only  in  circuit  with  a  battery  B  and  the  low 
resistance  primary  winding  P  of  an  induction  coil. 
The  variations  in  the  transmitter  resistance  now 
form  a  very  large  percentage  variation  in  the  cir- 
cuit resistance  and  great  fluctuations  in  the  current 
are  therefore  produced.  These  fluctuations  in  the 
primary  current,  as  explained  in  Chapter  V  of  this 

[96] 


From  Telegraph  to  Telephone 

book,  induce  fluctuating  secondary  currents  in  the 
S  winding  of  the  coil,  which  pass  out  over  the  line 
and  exactly  reproduce  every  tiny  tremor  of  the 
transmitter  diaphragm  in  the  diaphragm  of  the  dis- 
tant receiver  R.  That  is,  the  line  current  is  now  only 
the  fluctuating  part  of  the  transmitter  current,  and 
this  fluctuation  is  much  greater  than  when  the 
transmitter  is  directly  in  the  high-resistance  line 
circuit. 

The  receiver,  transmitter,  and  induction  coil  are 
of  course  merely  the  elements  of  the  wonderful  sys- 
tem of  telephones  which  now  makes  the  United 
States  little  more  than  a  great  neighborhood.  In 
the  central  station  switchboards,  in  the  transcon- 
tinental lines,  and  even  in  the  wall  and  desk  sets  arc 
inventions  of  the  highest  order,  made  by  pioneers 
whose  individual  names  are  lost  in  that  of  their 
company.  But  these  must  be  left  for  the  con- 
sideration of  the  specialist,  being  a  result,  rather 
than  a  part  of  the  development,  of  the  telegraph 
into  the  telephone. 


[97] 


IX 

THE  ELECTRIC  ARCH 

JUST  when,  where,  or  by  whom  the  electric  light 
was  first  seen  is  unknown.  But  whether  a 
primitive  man  of  the  warmer  zones  first  sufficiently 
overcame  his  fear  of  the  growling  thunder  to  look 
the  storm  cloud  in  the  face  and  see  the  lightning 
flashes,  or  whether  an  inhabitant  of  one  of  the 
regions  toward  the  poles  had  previously  seen  the 
beautiful  electrical  glow  which  we  of  the  northern 
hemisphere  call  the  northern  lights,  it  is  certain 
that  the  observation  must  have  been  made  very  near 
the  beginning  of  things,  and  that  electric  light, 
next  to  that  of  the  sun  and  stars,  is  the  oldest 
known  to  man. 

Of  the  electric  light  produced  directly  by  man, 
however,  the  first  record  is  found  in  the  work  of 
Otto  von  Guericke,  the  ingenious  Mayor  of  Magde- 
burg, whose  sulphur  ball  electrical  machine  is 
described  and  illustrated  in  the  first  chapter.  After 
the  ball  was  well  rubbed  with  the  palm  of  his  hand 
Von  Guericke  found  that  in  a  darkened  room  a 
glowing  light  enveloped  it,  which  increased  with 
[98] 


The  Electric  Arch 

further  friction  —  but  the  analogy  to  the  northern 
lights  escaped  him.  In  1680,  when  this  electric 
glow  light  had  become  one  of  the  commonplace 
experiments,  Robert  Hooke  observed  a  new  phe- 
nomenon —  "  the  more  you  rub  it  the  more  it  shines, 
and  any  little  stroke  upon  it  with  the  nail  of  one's* 
finger  when  it  so  shines,  will  make  it  seem  to  flash." 
This  flash  was  the  electric  spark. 

Sparks  of  greater  and  greater  magnitude  were 
produced  as  the  electrical  machines  were  improved, 
and  the  Ley  den  jar  was  discovered  and  developed, 
until  in  1749,  as  we  have  seen,  Franklin  included 
in  his  analysis  of  the  similarity  between  the  spark 
and  lightning,  "  Giving  light,  color  of  the  light, 
crooked  direction,  .  .  .  melting  metals,  firing 
inflammable  substances,  etc."  Thus  he  recognized 
clearly  that  the  electric  discharge  could  supply  both 
light  and  heat. 

From  this  time  on  the  spark  took  .perhaps  the 
foremost  place  among  well  known  electrical  phe- 
nomena, and  it  was  most  natural  therefore  that  it 
should  be  one  of  the  first  tests  applied  to  the 
product  of  Volta's  cell  to  investigate  the  identity 
of  the  new  with  the  old  electricity.  For  some 
months  no  results  were  obtained.  Wires  even  when 
brought  very  close  together  from  the  terminals  of  a 
cell  generating  one  or  two  volts,  refused  to  show 
any  spark  and  the  conviction  gradually  spread 

[99] 


Electricity:   Its  History  and  Development 

that  there  was  some  essential  difference  between 
Voltaic  and  frictional  electricity.  We  know  now 
that  a  pressure  of  at  least  35,000  volts  is  required 
to  pass  a  spark  through  1  inch  of  air,  and  hence, 
that  the  frictional  electric  machines  which  even  in 
small  sizes  generate  from  10,000  to  perhaps  400,- 
000  volts  were  the  only  early  apparatus  capable  of 
producing  sparks ;  but  it  was  not  until  the  time  of 
Faraday  that  this  view  prevailed,  and  the  identity 
of  all  forms  of  electricity  was  recognized.  Although 
the  early  experimenters  thus  worked  with  batteries 
of  insufficient  pressure  to  cause  sparks  to  jump 
across  even  the  shortest  distances  in  air,  it  was  soon 
found  that  when  a  circuit  through  which  a  current 
was  flowing  was  suddenly  broken  a  tiny  spark 
appeared  for  an  instant  at  the  break,  and  that  this 
spark  varied  in  color  with  the  material  of  which  the 
break  contacts  were  composed.  As  larger  batteries 
were  constructed  this  new  spark  experiment  was 
performed  with  more  spectacular  results,  until  in 
1809  Sir  Humphry  Davy  thought  it  of  sufficient 
interest  for  a  public  demonstration,  which  was 
described  in  a  contemporary  work  by  Singer,  as 
follows : 

With  a  large  apparatus  employed  at  the  Koyal  Institu- 
tion, which  extends  to  2,000  pairs  of  4-inch  plates  (2,000 
cells  of  battery,  that  is),  points  of  charcoal  were  brought 
within  a  thirtieth  or  fortieth  of  an  inch  of  each  other 

[100] 


The  Electric  Arch 

before  any  light  was  evolved;  but  when  the  points  of 
charcoal  had  become  intensely  ignited,  a  stream  of  light 
continued  to  play  between  them  when  they  were  gradually 
withdrawn  even  to  the  distance  of  near  four  inches.  The 
stream  of  light  was  in  the  form  of  an  arch,  broad  in  the 
middle  and  tapering  toward  the  charcoal  points;  it  was 
accompanied  by  intense  heat,  and  immediately  ignited  any 
substance  introduced  into  it.  Fragments  of  diamond  and 
points  of  plumbago  disappeared,  and  seemed  to  evaporate 
even  when  the  experiment  was  made  in  an  exhausted 
receiver;  though  they  did  not  appear  to  have  been  fused. 
Thick  platinum  wires  melted  rapidly,  and  fell  in  large 
globules;  the  sapphire,  quartz,  magnesia,  and  lime  were 
distinctly  fused. 

Even  today  a  better  description  can  hardly  be 
given  of  the  phenomena  of  the  electric  arch,  or,  as 
Davy  subsequently  renamed  it,  the  electric  arc. 
Only  in  one  particular  is  there  any  mistake  —  the 
light  did  not  come  mainly  from  the  arch  of  glowing 
carbon  vapor  which  served  to  conduct  the  current 
from  the  positive  charcoal  point  to  the  negative, 
but  from  the  intensely  hot  point  of  the  positive 
charcoal  itself.  Whatever  the  exact  source  of  the 
light  it  was  apparent  that  here  was  the  possibility 
of  an  artificial  illuminant  far  more  brilliant  even 
than  the  much  discussed  coal  gas  with  which  Wm. 
Murdock  had  but  lately  succeeded  in  lighting  one 
or  two  houses  in  Birmingham.  Inventors  followed 
hard  in  the  track  of  Davy,  and  various  forms  of 
mechanism  were  produced,  but  all  these  early 
attempts  to  design  an  arc  lamp  were  far  from  sue- 
[101] 


Electricity:   Its  History  and  Development 

cessful.  Many  difficulties  were  encountered  almost 
at  the  start,  for  not  only  were  the  charcoal  points 
consumed  very  rapidly,  but  a  very  considerable  bat- 
tery was  required,  and  all  the  early  cells  were  both 
expensive  and  most  unreliable  in  action.  The 
problem  proved  so  complex,  indeed,  that  illumina- 
tion by  coal  gas  forged  ahead  until  by  the  very 
success  of  the  gas  industry  one  of  the  missing  arc 
materials  was  provided,  and  electric  lighting  ob- 
tained a  new  impetus. 

In  1840  Bunsen  invented  a  process  whereby 
finely  ground  carbon  mixed  into  a  paste  with 
molasses  could  be  molded  into  any  desired  form 
and  then  subjected  to  a  high  temperature,  thereby 
producing  rods  or  plates  as  desired.  Now  the  car- 
bon left  in  the  retorts  after  the  volatile  components 
of  the  coal  were  driven  off  in  the  process  of  gas 
manufacture  was  found  to  be  just  the  material 
required  to  form  the  finely  ground  carbon  powder, 
and  carbon  plates  made  therefrom  and  used  in  an 
improved  battery,  also  developed  by  Bunsen,  gave 
a  much  cheaper  and  more  reliable  source  of  elec- 
trical current  than  any  previously  developed,  while 
the  same  material  molded  into  rods  formed  the 
slow-burning  arc  carbons  still  used  in  modern 
lamps. 

In  1844,  Deleuil  and  Archereau  produced  two 
lamps  which  were  installed  in  prominent  squares  of 
[  102  ]! 


The  Electric  Arch 

Paris  and  caused  very  considerable  excitement;  but 
after  a  few  weeks'  intermittent  operation  it  was 
found  that  even  should  the  mechanism  be  sufficiently 
improved  to  give  promise  of  reasonably  continuous 
service,  the  battery  supply  of  electric  current  was 
still  much  too  expensive  for  an  economical  light 
source.  Again,  then,  progress  was  stopped  by 
the  need  of  an  efficient  electric  supply,  and  again 
new  inventions  appeared  opportunely.  Electric 
generators  were  already  in  course  of  development 
from  the  early  models  of  Faraday,  and  in  1866  a 
sufficiently  satisfactory  machine  for  converting 
mechanical  rotation  into  electric  current  had  been 
constructed  to  warrant  the  installation  of  electric 
arcs  in  a  few  lighthouses  in  England  and  France, 
and  even  the  lighting  of  Prince  Napoleon's  yacht 
by  electricity. 

The  mechanism  of  the  arc  lamp  itself  was  still 
necessarily  complex. 

To  start  or  strike  the  arc,  the  carbons  must  first 
be  brought  into  contact  and  then  gradually  sep- 
arated to  that  distance  which  is  found  best  for  effi- 
cient light  production  —  in  modern  lamps  from 
%"  to  %"  according  to  the  type  of  arc.  Then,  as 
the  carbons  are  burned  in  the  intense  heat,  just  as 
coal  is  burned  on  a  grate,  the  arc  becomes  longer 
and  longer,  and  requires  more  and  more  voltage  to 
maintain  it,  until  a  point  is  reached  where  the  gen- 
[103] 


Electricity:   Its  History  and  Development 

erator  can  no  longer  supply  the  necessary  pres- 
sure, and  the  arc  goes  out,  or,  if  the  generator 
pressure  is  sufficiently  high,  the  arc  consumes  so 
much  energy  and  sends  out  so  much  heat  that  the 
lamp  is  destroyed.  Hence  a  mechanism  must  be 
supplied  for  moving  the  carbons  together,  or  feed- 
ing the  carbons,  at  such  a  rate  that  the  best  length 
of  arc  is  always  maintained. 

In  addition  to  these  confusing  requirements  the 
early  inventors  were  perplexed  by  one  of  the  nat- 
ural characteristics  of  the  arc.  In  an  ordinary 
resistance  like  that  of  a  length  of  wire,  which  we 
discussed  when  referring  to  Ohm's  law,  a  single 
definite  current  through  the  wire  corresponds  to  a 
definite  electrical  pressure  across  it ;  or,  if  the  pres- 
sure is  increased,  the  current  increases  until  a  value 
is  reached  such  that  this  new  current  multiplied  by 
the  resistance  just  equals  the  new  pressure,  and 
equilibrium  is  again  attained.  In  the  electric  arc, 
however,  the  resistance  is  found  to  vary  with  the 
current.  If  pressure  across  the  arc  is  increased 
the  current  increases,  normally  at  first,  but  in  so 
doing  lowers  the  resistance  so  that  the  current  still 
further  increases,  and  thus  still  further  lowers  the 
resistance,  the  process  continuing  until  the  maxi- 
mum current  which  the  generator  can  supply  is 
reached.  In  other  words,  the  arc  is  unstable.  Of 
all  these  difficulties  the  last  was  the  first  to  be  met 
[104] 


The  Electric  Arch 

satisfactorily,  a  result  achieved  by  connecting  the 
arc  lamps  in  series  and  supplying  them  from  a 
machine  so  designed  that  only  a  predetermined 
value  of  the  current  was  supplied,  no  matter  what 
the  resistance  of  the  circuit.  These  machines  are 
still  used,  the  design  being  such  that  as  the  resist- 
ance of  the  connected  circuit  to  the  machine 
decreases  the  voltage  supplied  by  the  machine 
decreases  proportionately,  and  vice  versa.  This 
means,  of  course,  that  as  more  lamps  are  added  in 
series  and  thus  more  resistance  introduced  into  the 
circuit,  the  pressure  across  the  machine  and  the 
pressure  supplied  to  the  circuit  increases,  and  thus 
the  number  of  lamps  supplied  by  one  machine  is 
limited  by  the  maximum  pressure  for  which  a 
machine  can  be  safely  built  or  which  can  be  safely 
used  in  cities. 

But  although  the  question  of  instability  was 
solved  quite  early  by  Brush  and  others,  as  just 
outlined,  the  difficulties  in  striking  and  feeding  the 
arc  continued  to  impair  the  operation  of  arc  lamps 
for  many  years,  and  it  is  only  during  the  last 
decade  that  perfect  operation  has  been  attained. 
The  fundamental  principles  were  discovered  by 
Hefner  von  Alteneck  and  embodied  in  the  Siemens 
&  Halske  lamp  constructed  as  shown  in  Figure  20. 
In  this  lamp  the  main  current  flows  from  L  through 
the  series  coil  R  and  thence  through  the  lever  ca 
[105] 


Electricity:   Its  History  and  Development 

r.nd  carbons  g  h  to  Lj.  The  carbon  g  is  held 
against  h  by  gravity  until  current  begins  to  flow, 
when  the  coil  R  pulls  the  iron  core  c  attached  to 
the  end  of  the  carbon  lever  ca,  down  into  R  by  rea- 
son of  the  magnetism  produced  by  R,  and  the  arc 
is  thus  struck.  As  the  carbons  burn  away  the 
resistance  of  the  arc  stream  increases,  and  since  the 
current  is  maintained  constant  by  the  generator,  the 
pressure  from  L  to  La  increases  and  more  and  more 
current  flows  through  the  coil  T  until  the  magnetic 
pull  of  this  coil  becomes  sufficiently  strong  to  raise 
the  core  c.  As  this  core  rises,  however,  the  arc 
length  is  reduced  and  thereby  the  pull  of  coil  T 
gradually  decreases  until  a  condition  is  reached 
such  that  the  drop  across  the  arc  is  just  sufficient 
to  maintain  the  current  through  T  which  is  required 
for  the  corresponding  position  of  core  c.  By 
proper  adjustments  this  position  may  be  made  to 
correspond  to  the  desired  arc  length  and  the  two 
coils  or  solenoids  T  and  S  will  maintain  an  arc  of 
constant  length  until  the  carbons  are  consumed. 

Many  improvements  and  modifications  of  this 
design  have  been  made,  until  the  arc  lamp  of  today 
is  one  of  the  most  effective  of  electrical  devices. 
Prominent  among  the  changes  which  have  led  to  a 
notable  advance  is  the  use  of  an  inner  globe  enclos- 
ing the  arc  in  a  confined  space  to  which  air  is 
admitted  very  slowly,  thus  greatly  restricting  the 

[106] 


Fig.   20.      Mechanism    of   the   first   successful   arc    lamp 


The  first  electric  heating  device — a  spark  used  to  ignite 

ether  [Page  108 


The  Electric  Arch 

combustion  of  the  carbons  and  thereby  decreasing 
the  rate  of  consumption  to  about  one-eighth  of  that 
in  the  open  air.  These  enclosed  arcs  require  trim- 
ming or  replacement  of  the  burnt  carbons  only 
once  a  week  instead  of  every  day,  and  this  longer 
life  greatly  decreases  the  expense  and  bother  of 
maintenance.  More  recently  the  so-called  flaming 
arcs  have  been  developed  in  which  the  carbons  arc 
impregnated  with  various  substances  which  pass 
into  the  conducting  arc  stream  and  render  it  very 
highly  luminous,  thereby  increasing  the  amount  of 
resultant  light  several  hundred  per  cent.  A  par- 
ticularly efficient  arc  has  been  invented  by  Dr. 
Steinmetz  —  the  luminous  arc  —  in  which  only  one 
electrode  is  consumed,  this  electrode  being  formed 
of  iron  and  titanium  compounds  giving  off  a  beau- 
tiful luminous  gas  and  having  an  extremely  long 
life. 

The  stream  of  light  from  Davy's  arc  has  thus 
spread  and  intensified  until  it  has  become  one  of 
the  necessities  of  modern  city  life,  but  in  the  mean- 
time what  has  been  done  with  the  characteristic 
which  apparently  most  impressed  Davy  and  his  con- 
temporaries, the  intense  heat  of  the  arc? 


[107] 


THE  HEAT  OF  NIAGARA 

SOME  relation  between  heat  and  electricity  began 
to  be  suspected  about  the  middle  of  the 
eighteenth  century  when  amateur  scientists  every- 
where eagerly  took  up  the  fascinating  experiments 
made  possible  by  the  discovery  of  the  Ley  den  jar. 
The  fine  ladies  of  London  crowded  the  rooms  of 
the  Royal  Society  to  see  tiny  dishes  of  ether  or 
alcohol  burst  into  flame  when  an  electric  spark  was 
discharged  near  the  surface  of  the  liquid,  or  to 
watch  with  polite  curiosity  at  the  thinnest  of  iron 
wires  melted  to  incandescent  globules  when  an  elec- 
tric discharge  passed  through  them.  By  1749,  four 
years  after  the  discovery  of  the  jar,  "  melting 
metals  "  and  "  firing  inflammable  substances  "  had 
become  two  of  the  best  known  attributes  of  the 
electric  spark ;  but  aside  from  the  pregnant  parallel 
which  Franklin  drew  between  these  effects  and  those 
of  lightning,  no  practical  applications  were  made. 
Sixty  years  later,  1809,  the  fine  ladies  of  London 
again  are  crowding  the  lecture  hall  of  the  Royal 
Society,  as  did  their  great-grandmothers,  to  see  the 
[108] 


The  Heat  of  Niagara 

wonderful  change  from  electricity  to  heat ;  but  now 
the  experiments  are  performed  by  Sir  Humphry 
Davy,  and  the  results  of  the  electric  arc  are  not 
merely  the  melting  of  thin  iron  wires,  but,  as  stated 
in  the  last  chapter,  "  Thick  platinum  wires  melt 
rapidly  and  fall  in  large  globules;  the  sapphire, 
quartz,  magnesia,  and  lime  are  distinctly  fused." 
Electricity  could  produce  temperatures  in  the  arc 
entirely  unattainable  by  any  other  means.  Under 
the  skilled  guidance  of  Davy  and  his  associates  the 
new  source  of  heat  was  employed  in  a  few  chemical 
investigations;  but  as  in  all  applications  of  elec- 
tricity, the  voltaic  cell  was  much  too  expensive  for 
any  extended  practical  use,  and  it  was  not  until  the 
production  of  the  generator  that  the  value  of 
electric  heat  became  apparent. 

Progress  was  retarded  too  by  the  theory  then 
prevailing  as  to  the  nature  of  heat,  which  was 
assumed  to  be  an  emission  of  tiny  particles  of  a 
substance  called  "  caloric."  The  electric  spark  or 
voltaic  current  in  passing  through  a  wire  was  sup- 
posed to  disengage  caloric  from  the  substance  of 
the  wire,  which  caloric,  striking  the  investigator's 
hand  or  some  other  temperature  indicator,  produced 
the  effects  of  heat.  Various  investigations  were 
undertaken  during  the  first  half  of  the  last  century 
to  show  the  relation  between  quantity  of  electricity 
passing  and  quantity  of  caloric  disengaged,  but  it 
[109] 


Electricity:   Its  History  and  Development 

was  not  until  1842,  when  the  Englishman  Joule 
made  his  classic  investigations  on  the  relation 
between  mechanical  energy  and  heat,  that  the  real 
advance  began. 

Joule  first  proved  that  if  an  apparatus  were 
arranged  so  that  a  weight  falling  through  a  con- 
siderable height  could  be  made  to  turn  a  paddle 
wheel  in  a  vessel  of  water  the  temperature  of  the 
water  would  be  raised  and  that  the  rise  in  water 
temperature  always  bore  a  fixed  relation  to  the 
work  done  by  the  weight  in  turning  the  wheel.  The 
quantity  of  heat  necessary  to  raise  the  temperature 
of  one  pound  of  water  one  degree  Fahr.  being  taken 
as  one  heat  unit,  this  amount  of  heat  was  produced 
through  the  friction  of  the  water  by  a  weight  of 
10  Ib.  falling  77.8  feet,  by  a  weight  of  100  Ib. 
falling  7.78  feet  or  by  any  other  combination  of 
weight  and  distance  which  gives  778  ft.  Ib.  of  work. 
The  mechanical  work  done  by  a  moving  mass  was 
thus  shown  to  be  exactly  equivalent  to  heat;  and 
as  philosophers  discussed  this  result  they  began  to 
believe  that  the  motion  of  the  weight  which  pro- 
duced motion  of  the  paddle  wheel  could  ultimately 
produce  perhaps  nothing  but  motions,  and  so  came 
to  be  accepted  the  modern  theory,  that  heat  is  a 
motion  of  the  minute  particles  or  molecules  which 
are  believed  to  compose  all  matter. 

Having  shown  that  the  energy  of  heat,  or  the 
[110] 


The  Heat  of  Niagara 

ability  of  heat  to  perform  work,  was  thus  merely  a 
form  of  the  energy  possessed  by  all  moving  bodies, 
from  sand  grains  to  cannon  balls,  Joule  turned  his 
attention  to  establishing  the  relation  between  heat 
and  the  electric  current.  For  these  experiments 
he  used  an  apparatus  which  Lenz  afterward  modi- 
fied to  the  form  shown  in  Figure  21,  consisting  of  a 
coil  of  resistance  wire  enclosed  in  a  vessel  of  water 
with  a  convenient  arrangement  for  passing  electric 
current  through  the  wire  and  for  reading  the  tem- 
perature of  the  water.  With  this  apparatus,  called 
the  current  calorimeter,  the  first  relation  to  be  dem- 
onstrated was,  that  no  matter  what  size  or  length 
of  wire  was  used,  no  matter  how  small  the  current 
or  how  short  the  time  of  flow,  some  heat  was 
always  produced.  In  other  words,  no  electric  cur- 
rent can  flow  in  any  circuit  without  some  of  its 
energy  being  converted  into  useless  heat  and  this 
heat  loss  is,  therefore,  inevitably  present  in  every 
transmission  line,  in  every  house-lighting  circuit,  in 
every  application  of  electricity.  By  careful  meas- 
urements Joule  finally  deduced  and  Lenz  verified 
the  relation,  now  known  as  Joule's  law,  that  the 
heat  generated  in  a  wire  is  proportional  to  the 
square  of  the  amount  of  current  flowing  multiplied 
by  the  resistance  of  the  wire  and  the  time  the  cur- 
rent flows.  That  is,  if  we  double  the  current  flow- 
ing through  a  given  wire  we  get  four  times  as 
[111] 


Electricity:   Its  History  and  Development 

much  heat ;  if  the  current  remains  constant  but  the 
wire  is  made  twice  as  long,  thereby  doubling  the 
resistance,  twice  as  much  heat  will  be  produced; 
while  if  resistance  and  current  strength  remain 
unaltered  but  the  time  of  flow  is  doubled  the  quan- 
tity of  heat  will  also  be  doubled. 

It  is  important  to  understand  this  pioneering  of 
Joule,  for  with  electric  current  equivalent  to  heat, 
and  heat  equivalent  to  mechanical  work,  the  relation 
between  electric  energy  and  mechanical  work  soon 
became  evident.  Expressed  in  abbreviated  form, 
Joule's  law  is, 

Heat  =  Current  X  Current  X  Resistance  X  Time; 
but  by  Ohm's  law,  Current  X  Resistance  =  Pres- 
sure, so  that  we  may  rewrite  Joule's  law, 

Heat  =  Current  X  Pressure  X  Time; 
and  as  Heat  produced  means  mechanical  work  done, 

Work  ===  Current  X  Pressure  X  Time; 
or,  in  modern  electrical  units, 

Work  =  Amperes  X  Volts  X  Seconds. 

The  work  that  is  done  by  electricity  in  forcing  a 
current  through  a  wire  or  any  other  electrical  cir- 
cuit thus  is  shown  to  be  equal  to  the  product  of  the 
pressure  necessary  to  cause  the  current  to  flow,  the 
strength  of  the  current,  and  the  time  the  operation 
continues. 

In  many  cases,  however,  it  is  necessary  to  know 
[112] 


The  Heat  of  Niagara 

not  only  how  much  work  is  done,  but  how  fast  it 
is  done  —  how  much  work  is  done  in  one  second. 
Indeed,  in  stating  the  size  of  a  steam  engine  or  a 
motor  or  any  other  source  of  mechanical  energy, 
the  attainable  rate  of  work  or  the  power  is  gener- 
ally the  figure  desired.  Evidently  this  rate  is  the 
total  amount  of  work  done,  divided  by  the  time  it 
takes  to  do  it ;  or,  since  Work  =  Volts  X  Amperes 
X  Seconds,  the  rate  of  work  equals  the  product  of 
the  volts  and  amperes  multiplied  by  the  seconds  and 
divided  by  the  seconds,  which  is,  of  course,  merely 
the  product  of  the  volts  and  amperes.  Hence,  we 
have  finally, 

Power  =  Volts  X  Amperes. 

These  statements  are  strictly  true  of  all  work 
and  power  relations  in  direct-current  circuits,  and 
of  all  heat  production  in  alternating-current  cir- 
cuits, but  have  to  be  somewhat  modified  for  alter- 
nating currents  converted  into  forms  of  energy 
other  than  heat.  This,  however,  introduces  ques- 
tions rather  too  complex  for  the  present  discussion ; 
it  is  sufficient  to  remember  that  in  alternating-cur- 
rent circuits  the  product  of  volts  and  amperes 
frequently  shows  an  apparent  power  greater  than 
the  true  power. 

The  unit  rate  of  work  is  taken  as  that  obtaining 
in  an  apparatus  where  one  volt  is  causing  a  cur- 
[113] 


Electricity:   Its  History  and  Development 

rent  of  one  ampere  to  flow,  and  this  rate  of  work 
is  called  the  watt.  If  work  is  being  done  1,000 
times  as  fast  as  this,  the  rate  of  work  is  said  to  be 
one  kilowatt;  and  the  amount  of  work  done  when 
this  kilowatt  rate  continues  for  an  hour  is  called 
one  kilowatt-hour,  and  is  used  as  the  basis  for  sell- 
ing electric  energy.  Very  exact  measurements  have 
been  made  of  the  quantity  of  heat  generated  by  one 
kilowatt  hour  of  electrical  work,  and  from  these 
data,  and  those  obtained  in  careful  repetitions  of 
Joule's  original  experiments  on  the  heat  units  gen- 
erated by  a  falling  weight,  the  numerical  relation 
of  the  electrical  and  mechanical  units  can  be  accu- 
rately computed.  In  this  way  it  is  found  that  a 
one-horsepower  engine  will  do  the  same  amount  of 
work  in  one  hour  as  will  an  electric  generator  pro- 
ducing 0.746  of  a  kilowatt  hour,  or  that  an  electric 
power  of  746  watts  is  the  equivalent  of  the  mechan- 
ical rate  of  work  called  one  horsepower. 

With  the  law  connecting  heat  and  electricity 
fully  developed  the  production  of  apparatus  suit- 
able for  converting  electric  current  into  heat  be- 
came merely  a  question  of  mechanical  design,  as  is 
attested  by  the  many  forms  of  successful  stoves, 
cooking  utensils,  flat  irons,  soldering  irons,  and 
other  devices  now  in  use.  In  all  this  apparatus  the 
heat  as  fast  as  it  is  generated  is  dissipated  through 
conduction  by  the  surrounding  air  or  by  radiation 
[114] 


The  Heat  of  Niagara 

to  other  bodies,  or  is  absorbed  by  the  material  upon 
which  work  is  being  done;  and  in  consequence  the 
size  of  apparatus  to  be  used  for  any  process  will 
depend  on  the  rate  of  heat  dissipation  which  must 
be  maintained  rather  than  on  the  total  quantity  of 
heat  required. 

In  almost  all  electrical  heating  devices  heat  is 
produced  in  a  wire  or  other  metallic  conductor  hav- 
ing a  high  resistance  per  unit  of  length,  and  it  has 
been  found  that  the  rate  at  which  each  unit  length 
of  such  a  wire  gives  off  heat  is  proportional  to  its 
temperature.  If  then  the  rate  of  generating  heat 
is  gradually  increased  by  forcing  more  and  more 
current  through  the  heating  coil  or  wire  the  tem- 
perature of  the  wire  will  also  increase  until  it 
reaches  such  a  degree  that  the  wire  melts  —  an 
action  exemplified  in  the  fuse  wire  commonly  placed 
in  series  with  a  circuit  which  it  is  desired  to  open 
when  the  current  exceeds  a  certain  value.  More 
heat,  however,  can  be  dissipated  per  unit  length  if 
the  wire  is  surrounded  by  a  better  heat  conductor 
than  air,  and  in  many  devices  the  coils  are  im- 
bedded in  enamels  which  serve  not  only  to  increase 
the  rate  of  heat  dissipation  but  also  to  insulate  the 
various  convolutions  of  the  winding  and  to  protect 
the  hot  wire  surfaces  from  the  attacks  of  atmos- 
pheric oxygen. 

In  all  this  class  of  apparatus  the  temperatures 
[115] 


Electricity:   Its  History  and  Development 

produced  are  comparatively  low,  the  great  advan- 
tages of  electric  heat  being  found  in  the  ease  with 
which  it  is  generated  at  the  point  of  use,  the  ab- 
sence of  all  the  smoke  or  hot  gases  inevitably  pres- 
ent with  burning  fuel,  and  the  close  control  of 
temperature  readily  obtained  by  controlling  current 
strength. 

But  electric  heat  has  another  field  in  which  it  is 
unique  —  the  production  of  very  high  tempera- 
tures in  the  various  forms  of  electric  furnace.  The 
most  usual  type  of  furnace,  shown  in  Figure  22,  is  a 
direct  development  of  Davy's  experiment,  the  arc 
being  formed  between  large  electrodes  just  over  a 
crucible  containing  the  material  to  be  heated  and 
the  whole  enclosed  in  a  small  chamber  with  thick 
walls  of  heat-insulating  material.  A  temperature 
of  over  3,500°  Centigrade,  nearly  twice  that  at- 
tainable in  any  fuel  furnace,  can  readily  be  reached, 
and  with  this  equipment  electro-chemists  have  pro- 
duced such  substances  as  the  abrasive  carborundum ; 
graphite  of  great  purity;  calcium  carbide  for  the 
generation  of  acetylene  gas ;  and  the  highest  grades 
of  steel.  Some  of  these  materials  are  made  with 
greater  economy  in  the  resistance  furnaces,  in  which 
the  substance  to  be  heated  is  used  to  carry  the  cur- 
rent, as  shown  in  Figure  22% ,  and  thus  gradually 
raised  in  temperature  to  any  desired  degree.  In 
this  type  also  a  heat-insulating  chamber  is  used  and 
[116] 


Fig.    21.      Lenz's    current    calorimeter    with    which    he 
verified  the  relation  between  heat  and  electricity 

[Page  111 


Fig.  22.     The  arc  type  of  electric  furnace 


Fig.  22%.     The  first  commercial  application  of  electric 
heat.      The   Cowles  resistance   furnace 


The  Heat  of  Niagara 

the  temperature  attainable  is  limited  only  by  the 
melting  point  of  the  walls  or  of  the  electrodes  used 
to  conduct  the  current  to  the  material. 

A  contemporary  of  Davy,  after  witnessing  his 
demonstration  of  the  heat  of  the  arc,  wrote  that  it 
was  the  most  brilliant  experiment  in  all  science. 
Today  the  waters  of  the  great  lakes  are  perform- 
ing this  experiment  at  Niagara  on  a  scale  which 
results  in  a  great  industry,  and  to  the  laurels  of 
the  pioneers  is  added  the  development  of  electric 
heat. 


[117] 


XI 
THE  BAMBOO  LIGHT 

ANY  solid  substance  will  send  out  light  if  it  is 
heated  to  a  sufficiently  high  temperature,  pro- 
vided, of  course,  that  it  is  not  destroyed  before  the 
necessary  temperature  is  reached.  The  experi- 
mental facts  upon  which  this  generalization  is  based 
began  to  be  accumulated  at  least  as  early  as  the 
iron  age,  and  for  many  centuries  it  has  been  one  of 
the  commonplaces  of  everyday  life.  No  sooner, 
then,  was  it  found  that  an  electric  current  heated 
the  conductor  through  which  it  passed  than  experi- 
ments were  made  in  the  attempt  to  develop  suf- 
ficient heat  to  cause  the  conductor  to  give  off  light, 
and  after  some  failures  the  prominent  electricians 
of  the  latter  half  of  the  eighteenth  century  could 
show  incandescent  wires  of  iron,  platinum,  and  even 
gold  and  silver. 

Contemporaneously  with  the  development  of  the 
electric  arc  light  this  second  form  of  electric  light 
claimed  the  attention  of  many  inventors  who  en- 
deavored so  to  arrange  an  incandescent  conductor 
that  it  would  withstand  high  temperature  for  a  con- 
siderable time;  or,  in  other  words,  have  a  sufficient 

[118] 


The  Bamboo  Light 

life  to  make  possible  its  application  as  a  commercial 
light  source.  As  early  as  1820  De  la  Rue  enclosed 
a  long  spiral  of  platinum  wire,  as  shown  in  Figure 
23,  in  a  glass  tube  from  which  the  air  could  be 
exhausted,  this  exhaustion  being  intended  to  pre- 
vent any  chemical  action  between  the  hot  platinum 
and  the  oxygen  of  the  air.  But  although  the  plati- 
num spiral  could  be  made  to  glow  brightly  for  a 
few  moments,  it  soon  melted  at  one  point  or  an- 
other and  had  to  be  replaced. 

Platinum  continued  to  be  the  favorite  material 
for  the  incandescent  conductor  until  1845,  when  a 
young  American,  J.  W.  Starr,  took  out  a  patent  in 
England  for  the  lamp  shown  in  Figure  24.  Starr 
used  a  strip  of  carbon  in  the  high  vacuum  existing 
at  the  top  of  a  barometer  tube.  His  lamp  gave 
such  promise  that  Faraday  is  said  to  have  shown 
enthusiastic  interest.  After  a  successful  exhibition 
of  a  candelabrum  containing  26  of  the  lamps,  one 
for  each  State  in  the  Union,  Starr,  who  was  but  25 
years  old,  died  on  his  return  voyage  to  America, 
and  the  commercial  development  of  his  lamp  was 
given  up.  But  he  had  clearly  stated  in  his  patent 
application  that,  "the  metal  found  most  advan- 
tageous to  use  is  that  which,  while  it  requires  a 
very  high  temperature  for  its  fusion,  has  but  a 
feeble  affinity  for  oxygen,  and  offers  a  great  re- 
sistance to  the  passage  of  an  electric  current"; 

[119] 


Electricity:   Its  History  and  Development 

and  he  had  demonstrated  the  practicability  of  em- 
ploying carbon,  so  that  for  the  next  thirty  years 
carbon  was  the  main  subject  of  experiment. 

Despite  the  numerous  modifications  which  were 
made  of  Starr's  lamp,  however,  and  the  frequent 
announcements  of  success  which  came  first  from 
France,  then  from  England,  then  from  Russia,  and 
so  on  over  the  scientific  world  and  back  again,  the 
real  incandescent  lamp  appeared  as  far  off  as  ever. 
Carbon  seemed  to  have  the  property  of  self-destruc- 
tion at  high  temperature,  for  with  the  best  vacuum 
then  obtainable  the  rods  gradually  disintegrated. 
In  consequence  complex  mechanisms  were  arranged 
within  the  lamps  to  replace  burnt  out  rods  with  new 
ones,  and  thus  certain  lamps  were  given  a  life  of 
several  hours !  As  the  carbons  required  such  fre- 
quent replacement  it  was  necessary  to  provide  globes 
which  could  be  easily  opened  and,  after  replenish- 
ing the  burners,  easily  exhausted;  therefore  the 
incandescent  lamps  made  before  1880  are  large, 
cumbersome  affairs  with  clamps  and  rubber  rings 
or  cement-filled  grooves  for  securing  air-tight 
joints,  and  projecting  stop-cocks  for  connection  to 
portable  air  pumps. 

And  then  came  Edison ! 

Edison's  attention  was  first  seriously  attracted  to 
the  problem  of  the  incandescent  light  by  the  com- 
mercial success  of  the  arc  light,  which  by  1878  had 
[120] 


The  bamboo  filament  Edison  lamp 


Fig.  23.     De  la  Rue's  platinum  light 


Fig.  24.     Starr's  lamp,  using  a  short,  thick  carbon 
barometer  tube 


Fig.  25.     Assembling  bulb  and  filament  for  welding 

[Pave  125 


Metallized  carbon  lamp  [Page  126 


The  Bamboo  Light 

taken  its  place,  in  this  country  at  least,  as  the  future 
street  illuminant.  To  Edison  it  was  evident  that 
the  lighting  of  small  interiors,  such  as  private 
rooms  and  stores,  was  a  much  more  important  field ; 
and  after  an  exhaustive  study  of  the  gas-lighting 
system  he  became  convinced  that  this  field  could  be 
successfully  covered  only  by  a  system  of  small  in- 
candescent lights  in  which  any  lamp  could  be  turned 
on  or  off  entirely  independent  of  any  other.  That 
is,  instead  of  the  series  system  which  had  been  uni- 
versally proposed  heretofore  and  in  which,  as  the 
current  passed  through  all  the  lamps  one  after  an- 
other, the  failure  of  any  one  served  to  interrupt  the 
circuit  and  thus  extinguish  all  the  lights,  Edison 
decided  to  develop  a  parallel  system.  In  this  sys- 
tem each  lamp  would  be  connected  between  the  pair 
of  wires  leading  to  the  generator,  so  that  there 
would  be  as  many  paths  for  current  to  flow  from 
the  positive  to  the  negative  wire  as  there  were 
lamps  connected,  and  the  failure  of  a  lamp  would 
thus  mean  merely  the  interruption  of  one  path  and 
would  not  affect  the  other  lights.  With  any  of  the 
lamps  previously  constructed  a  current  of  10  am- 
peres or  more  was  necessary  for  incandescence;  a 
parallel  system  of  connection  would  therefore  re- 
quire enormous  distributing  wires,  as  each  lamp 
added  would  increase  the  current  in  the  main  wire 
by  10  amperes,  and  a  hundred  lamps  in  parallel 

[121] 


Electricity:   Its  History  and  Development 

would  mean  distributing  wires  capable  of  carrying 
1,000  amperes  or  having  a  cross  section  of  nearly 
a  square  inch.  Hence,  to  make  a  parallel  system 
practical,  Edison  must  produce  an  incandescent 
light  which  would  not  only  have  a  reasonable  life 
but  which  would  require  much  less  current  than  any 
that  had  been  even  suggested  as  desirable. 

In  1878  the  attack  began  with  experiments  on 
tiny  strips  of  carbonized  paper  raised  to  incan- 
descence in  a  vacuum,  Edison's  idea  being  that  in 
order  to  reduce  the  current  required,  it  was  neces- 
sary to  reduce  the  amount  of  material  to  be  heated, 
but  these  primitive  paper  filaments  had  a  maximum 
life  of  fifteen  minutes,  and  after  weeks  of  effort  he 
was  disposed  to  accept  the  theory  of  the  self- 
destruction  of  carbon.  Turning  to  the  investiga- 
tion of  platinum  filaments  in  the  fall  of  1878  Edison 
concentrated  his  efforts  on  securing  and  maintain- 
ing a  better  vacuum,  and  in  the  course  of  certain 
trials  on  platinum  sealed  into  a  closed  glass  bulb  he 
discovered  that  the  life  was  greatly  improved  by 
heating  the  filament  to  incandescence  during  the 
process  of  exhausting  and  sealing.  This  has  been 
found  to  be  due  to  the  fact  that  certain  gases  are 
attached  to  the  surface  of  the  cold  wire  and  ab- 
sorbed in  its  substance  —  or  occluded  —  and  that 
when  the  wire  is  heated  these  are  given  off,  and,  of 
course,  in  the  older  lamps  they  immediately  de- 


The  Bamboo  Light 

stroyed  the  vacuum.  Even  with  these  improve- 
ments, however,  platinum  had  but  a  short  life,  for 
in  order  to  get  a  fair  light  it  had  to  be  operated 
near  its  melting  temperature.  Returning  to  his 
carbon  filament  experiments  to  determine  the  effect 
of  the  new  method  of  exhaustion  and  the  use  of  an 
all-glass  sealed  globe,  Edison,  on  October  21,  1879, 
produced  a  lamp  having  a  filament  of  carbonized 
cotton  sewing-thread  sealed  in  a  glass  globe  ex- 
hausted to  a  vacuum  of  one-thirty-thousandth  of 
an  atmosphere,  which  burned  for  4,0  hours.  The 
old  paper  filaments  were  then  tried  once  more  and 
proved  much  better  even  than  the  thread,  and  ar- 
rangements for  the  commercial  development  of  the 
lamp  were  at  once  begun. 

In  the  course  of  these  experiments  Edison  had 
found  that  although  reducing  the  cross  section  of 
the  filament  reduced  the  current  necessary  to  bring 
it  to  incandescence,  as  he  desired,  it  also,  of  course, 
reduced  the  surface  area  so  that  the  light  given  off 
per  inch  of  filament  length  was  decreased  in  pro- 
portion to  the  decrease  in  filament  diameter.  To 
get  the  amount  of  light  which  he  intended,  there- 
fore,—  sixteen-candlepower,  or  the  equivalent  of 
an  ordinary  gas  flame  —  it  was  necessary  to  in- 
crease the  length  of  the  filament,  and  thereby  its 
resistance,  to  such  a  degree  that  110  volts  were 
required  by  Ohm's  law  to  force  the  necessary  cur- 
[123] 


Electricity:   Its  History  and  Development 

rent  through  the  lamp.  In  this  way  the  pressure 
of  distribution  was  fixed  at  110  volts  —  a  magni- 
tude which  is  still  the  standard. 

The  first  hundred  lamps  were  strung  along  the 
streets  and  in  some  of  the  houses  of  Menlo  Park, 
soon  to  be  famous  the  world  over  as  the  birth- 
place of  the  Edison  lamp.  On  the  last  day  of  the 
year  1879,  evening  excursions  from  New  York 
brought  three  thousand  visitors  to  see  the  latest 
wonder  —  the  light  which  was  to  be  the  chief  factor 
in  making  this  the  age  of  electricity. 

But  although  the  paper  filaments  were  most  suc- 
cessful as  compared  with  all  preceding  attempts; 
although  the  lamps  gave  a  light  about  equivalent 
to  that  of  an  ordinary  gas  flame,  required  less  than 
an  ampere  of  current,  and  had  a  life  of  more  than 
a  hundred  hours ;  although  the  greatest  enthusiasm 
soon  prevailed  throughout  the  world  of  science  and 
the  problem  was  declared  finally  solved,  Edison  was 
not  satisfied.  The  life  of  the  lamps  was  still  too 
short  —  the  behavior  of  different  lamps  was  not 
sufficiently  uniform.  Night  and  day  he  and  his 
assistants  worked,  trying  every  conceivable  form  of 
paper  and  vegetable  fibres  until  several  thousand 
different  materials  had  been  made  into  filaments, 
tested,  and  found  no  better  than  the  original  paper. 
And  then  one  day,  in  the  spring  of  1880,  he  no- 
ticed the  strip  of  bamboo  used  to  bind  a  palm-leaf 


The  Bamboo  Light 

fan.  Straightway  he  made  filaments  out  of  that,  and 
thus  discovered  the  material  which  was  used  for  the 
several  millions  of  lamps  manufactured  during  the 
next  nine  years.  Having  found  bamboo  to  be 
good,  this  great  electrical  pioneer  enlisted  other 
men  dominated  by  the  world-old  pioneering  spirit 
to  go  to  every  bamboo-producing  part  of  the  earth 
and  find  that  bamboo  which  was  best.  Japan, 
Southern  Brazil,  Jamaica,  Cuba,  the  swamps  of 
Florida,  the  unknown  jungles  of  the  farthest  Ama- 
zon were  all  searched,  and  cases  upon  cases  of  speci- 
mens were  sent  back  for  test,  the  number  of  filament 
materials  investigated  nearing  6,000,  when,  in 
1889,  just  as  the  latest  explorer  returned  with  re- 
ports on  the  bamboos  of  India  and  the  Malay 
peninsula,  the  laboratory  pioneers  produced  an 
artificial  filament  material  which  proved  better 
than  any  natural  fibre  and  the  use  of  bamboo  was 
gradually  discontinued. 

All  carbon  lamps  made  today  are  of  the  artificial 
or  "  squirted  "  filament  type ;  the  process  of  manu- 
facture is  partially  illustrated  in  Figure  25.  Some 
natural  cellulose  fibre,  such  as  cotton,  is  dissolved 
in  a  suitable  liquid,  and  the  solution,  having  about 
the  consistency  of  molasses,  is  squirted  under  pres- 
sure through  a  fine  hole  into  another  solution  which 
immediately  hardens  the  thread  of  cellulose.  This 
tough  thread  is  then  cut  to  the  proper  lengths  and 
[125] 


Electricity:   Its  History  and  Development 

wound  on  forms  to  the  shape  desired  for  the  finished 
filaments.  Forms  and  cellulose  threads  are  next 
placed  in  ovens  and  the  cellulose  carbonized,  result- 
ing in  carbon  filaments  of  standard  size  and  of 
approximately  uniform  cross  section.  Exact  uni- 
formity of  cross  section  is  obtained  by  the  process 
known  as  "flashing,"  in  which  the  filaments  are 
brought  to  incandescence  with  electric  current  while 
surrounded  by  gasoline  vapor  or  some  other  gas, 
rich  in  carbon  and  readily  decomposed  bv  heat. 
As  the  filament  is  hotter  at  points  of  smaller  diame- 
ter, the  gas  is  decomposed  faster  and  more  carbon 
deposited  on  the  filament  surface  at  these  points 
until  perfect  equality  of  cross  section  is  attained, 
when  the  temperature  becomes  uniform.  The  de- 
posit of  carbon  then  proceeds  equally  along  the 
entire  length  of  the  filament  and  is  continued  until 
the  desired  diameter  is  reached.  After  the  flashing 
process,  filaments  of  the  better  grades  are  "  metal- 
lized" by  subjecting  them  to  the  high  temperature 
of  the  electric  furnace,  which  so  changes  the  sur- 
face carbon  that  it  acquires  metallic  characteristics 
and  can  be  operated  at  a  much  higher  temperature 
than  the  crude  carbon  deposited  in  the  flashing 
process.  All  filaments  are  cemented  to  two  short 
lengths  of  platinum  wire  which  in  turn  are  soldered 
to  two  copper  lead  wires  and  sealed  into  a  length  of 
glass  tubing  (1 — Figure  25),  platinum  being  nee- 
[126] 


The  Bamboo  Light 

essary  at  the  point  where  the  circuit  passes  through 
glass,  as  this  metal  expands  and  contracts  with  heat 
changes  at  the  same  rate  as  glass  and  so  maintains 
an  air-tight  seal  through  the  widest  variations  of 
temperature.  The  glass  tube  bearing  the  filaments 
is  now  introduced  into  the  globe  or  bulb,  and  the 
two  welded  together  (at  3  —  Figure  25),  after 
which  the  bulb  is  exhausted  through  a  small  tube 
(2 —  Figure  25)  at  its  tip  —  the  filament  being 
heated  to  expel  occluded  gases  as  above.  When  the 
desired  vacuum  is  reached  the  tube  is  sealed  off 
with  a  blowpipe,  and  the  lamp  is  then  ready  for 
mounting. 

While  this  process  of  manufacture  has  been  grad- 
ually growing  more  perfect,  however,  pure  science 
has  been  gaining  a  clearer  insight  into  the  relations 
between  the  heat  of  a  body  and  the  light  which  it 
gives  off;  and  now,  when  the  carbon  lamp  can  be 
produced  at  a  lower  cost  and  in  more,  perfect  form 
than  even  Edison  dared  hope,  a  new  filament  ma- 
terial, developed  along  the  lines  indicated  by 
science,  bids  fair  to  monopolize  the  market.  It  has 
been  known  for  many  years  that  the  higher  the 
temperature  of  a  body  the  higher  the  percentage 
that  its  light  radiations  bear  to  the  radiations  of 
heat,  which  inevitably  dissipate  the  greater  part  of 
the  energy  consumed  by  any  light  source.  Herein 
lay  the  fundamental  reason  for  the  use  of  the  most 
[127] 


Electricity:   Its  History  and  Development 

refractory  of  all  substances,  carbon,  for  an  incan- 
descent material.  But  recently,  scientific  investi- 
gations have  shown  that  although  carbon  can  be 
heated  to  a  higher  temperature  than  any  other 
known  substance  before  boiling  or  melting  —  a  tem- 
perature of  3,700  degrees  Centigrade  —  it  unfor- 
tunately begins  to  evaporate  at  about  1,800  degrees 
Centigrade,  so  that  this  latter  temperature  is  really 
the  limit  for  carbon  filament  incandescence.  Above 
this  point  the  carbon  rapidly  vaporizes  and  deposits 
a  black  film  over  the  inside  of  the  globe.  Knowing 
this,  it  at  once  became  evident  that  some  substance 
having  a  lower  melting  point  than  carbon  might 
still  be  operated  at  a  higher  temperature  if  it 
chanced  to  have  a  higher  evaporation  point,  and  in 
working  along  these  lines  the  rare  metals,  tantalum, 
osmium,  tungsten,  and  others  were  tried  success- 
fully. Tungsten  especially  meets  the  requirements, 
as  although  it  melts  at  3,200  degrees  Centigrade 
—  500  degrees  lower  than  carbon  —  it  does  not 
begin  to  evaporate  until  raised  nearly  to  the 
melting  point  and  consequently  can  be  operated  at 
such  a  high  temperature  that  it  produces  over  twice 
as  much  light  radiation  for  a  given  energy  con- 
sumption as  does  the  best  carbon  filament.  At  first 
the  tungsten  lamps  were  extremely  fragile,  for,  in 
order  to  meet  the  standard  110-volt  distribution 
pressure,  the  filament  diameter  in  a  20-candlepower 
[128] 


Tungsten   "wire   type"    lamp,   showing  lead    wires    (1), 
platinum  wires  through  glass  seal  (p),  filament  sup- 
port (s),  and  long,  continuous  wire  filament  (f) 


The  Bamboo  Light 

lamp  must  be  reduced  to  about  0.001  inch  —  less 
than  one-fifth  that  of  the  corresponding  carbon. 
Vrery  recent  improvements  in  the  manufacture  of 
the  tungsten  filaments,  however,  have  been  made, 
which  give  it  a  tensile  strength  four  or  five  times  as 
great  as  mild  steel,  and  it  will  undoubtedly  soon 
dominate  the  incandescent  lighting  field. 

The  extent  and  importance  of  this  field  is  indi- 
cated by  the  120,000,000  lamps  in  service  in  1910, 
consuming  $225,000,000  worth  of  electrical  en- 
ergy per  year  —  a  complete  justification  for  the 
men  who  risked  $40,000  in  order  that  Edison  might 
make  one  more  attempt  at  the  supposed  impossi- 
bility—  the  production  of  a  commercial  incan- 
descent light. 


[129] 


XII 
THE  ELECTRICAL  REVOLUTION 

"'T^HERE  they  go !  there  they  go !  we  have  suc- 
•*•  ceeded  at  last."  On  the  table  in  the  laboratory 
of  the  Royal  Institution,  September  3,  1821,  stood 
a  little  apparatus  very  similar  to  that  shown  in 
Figure  26,  consisting  of  a  vertical  glass  tube  closed 
at  both  ends  by  corks,  and  having  a  small  amount 
of  mercury  in  the  lower  end  through  which  one  pole 
of  a  bar  magnet  was  thrust,  while  from  the  upper 
cork  a  stiff  wire  was  loosely  hung  so  that  its  lower 
end  dipped  in  the  mercury.  Michael  Faraday  and 
his  brother-in-law,  George  Barnard,  had  just  com- 
pleted the  arrangement  a  moment  before  by  con- 
necting several  voltaic  cells  to  the  circuit  running 
through  the  hook  supporting  the  stiff  wire,  thence 
along  this  wire  to  the  mercury  pool  and  then  back 
to  the  battery.  And  now  as  Faraday  exclaimed, 
"  There  they  go,"  the  lower  end  of  the  wire  began 
to  move  slowly  and  jerkily  round  and  round  the 
magnet  pole.  Small  wonder  that  Faraday  "  danced 
about  the  table  with  beaming  face  " —  for  there  be- 
fore them  was  the  first  electric  motor,  the  mysterious 
[130] 


The  Electrical  Revolution 

source  of  motion  which  was  to  be  developed  until  to- 
day we  have  grown  so  accustomed  to  it  in  electric 
cars,  in  noiseless  automobiles,  and  in  the  almost 
numberless  applications  of  power  motors,  that  we 
have  nearly  forgotten  its  mystery  and  only  remem- 
ber its  wonderful  usefulness. 

Oersted  had  stated  in  1819,  almost  immediately 
after  his  discovery  of  the  deflection  of  a  magnetic 
needle  by  the  current  in  a  wire,  as  discussed  in  the 
fourth  chapter  of  this  book,  that  "  the  electric  con- 
flict acts  in  a  rotating  manner";  for,  said  he,  de- 
flections of  the  needle  in  opposite  directions  are 
obtained  when  it  is  held  first  above  and  then  below 
the  current-carrying  wire,  and  it  is  easiest  to  think 
of  this  as  due  to  a  force  acting  in  a  circle  about  the 
wire  axis.  But  Oersted  and  his  immediate  followers 
soon  forgot  this  brilliant  statement  of  the  truth  and 
wasted  their  experiments  on  the  assumed  but  purely 
fictitious  attraction  of  the  wire  for  the  needle. 

In  1820  Faraday  was  commissioned  to  write  a 
history  of  electro-magnetism  for  a  monthly  period- 
ical, and  in  his  thorough-going  way  he  repeated 
all  the  experiments  made  by  others  before  attempt- 
ing to  describe  them.  He  quickly  assured  himself 
that  the  force  between  the  magnet  and  wire  did  not 
produce  the  slightest  tendency  to  draw  them  to- 
gether or  push  them  apart,  but  rather  to  cause  the 
north  pole  to  rotate  in  one  direction  around  the 
[131] 


Electricity:   Its  History  and  Development 

wire  while  the  south  pole  was  urged  to  the  oppo- 
site direction  of  rotation.  In  other  words,  a  mag- 
net pulled  in  opposite  directions  at  its  poles  was 
merely  set  at  right  angles  to  the  wire  axis.  The 
magnet  as  a  whole  then  could  not  rotate,  but  if  one 
pole  could  be  obtained  without  the  other,  rotation 
should  result.  Eventually  he  found  it  easier  to 
take  advantage  of  Newton's  law  that  action  and 
reaction  are  equal,  or  to  allow  the  wire  to  move 
while  the  magnet  remained  stationary,  as  in  the 
apparatus  of  Figure  26,  the  arrangement  of  the 
device  limiting  the  reaction  of  the  current  in  the 
movable  wire  to  one  pole  of  the  magnet.  With 
this  apparatus  he  verified  his  expectation  that  the 
direction  of  revolution  could  be  reversed  by  re- 
versing the  direction  of  current  flow,  or  by  re- 
versing the  magnet  but  maintaining  the  current 
direction. 

The  relation  of  these  different  directions  is  best 
remembered  by  Fleming's  left-hand  rule  (Figure 
27),  which  states  that  if  the  thumb,  forefinger  and 
middle  finger  of  the  left  hand  are  held  so  that  each 
is  at  right  angles  to  the  other  two,  the  forefinger 
pointing  along  the  lines  of  force  and  the  middle 
finger  along  the  direction  of  current  flow,  then  the 
thumb  will  point  in  the  direction  of  motion.  Ap- 
plying this  to  Figure  26 :  if  the  north  pole  is  above 
the  mercury  surface  and  the  current  flows  down- 
[132] 


Fig.    26.     Faraday's    first    device 

for   showing  the   electrical 

revolution 


Fig.    28.      Lines   of   force   about   a   north   magnetic   pole 

(black  circle),  and  a   wire  carrying  current  down 

through  plane  of  paper    (white  circle) 

[Page  133 


Fig.    27.      Fleming's    "left-hand    rule"    for    finding   the 
direction  of  motion  of  a  conductor  when  the  direc- 
tion of  the  magnetic  field  and  of  the  current 

flow  are  known  [Page  132 


Fig.  29.     (a)  Rearrangement  of  Faraday's  device  using 

horseshoe    magnet 

(b)    Barlow's   wheel   developed    from    (a)    for   securing 
continuous  rotation  [Page  134 


The  Electrical  E evolution 

ward  along  the  wire,  as  the  lines  of  force  radiate 
from  the  pole  like  the  spokes  of  a  wheel,  we  find 
that  the  wire  will  rotate  in  a  clockwise  direction  as 
we  look  down  on  the  mercury  surface. 

But  why  does  it  rotate?  We  remember  that  ac- 
cording to  Faraday's  theory  of  lines  of  force 
(Chapter  IV)  these  lines  are  in  tension  along  their 
length  and  mutually  repel  each  other.  Does  the 
current  flowing  in  the  wire  call  into  play  either  this 
tension  or  repulsion  and  so  cause  rotation?  In 
Figure  28  we  have  an  iron-filing  diagram  of  the  lines 
of  force  about  a  north  magnetic  pole  and  a  wire  in 
which  a  current  is  flowing  downward  —  the  same 
conditions  we  assumed  for  Figure  26  —  and  here  we 
can  see  how  the  tension,  tending  to  pull  the  lines 
straight,  forces  the  wire  ahead ;  while  if  the  diagram 
were  perfect  we  should  see  that  the  lines  above  or 
behind  the  wires  are  crowded  together,  so  that  the 
mutual  repulsion  tends  also  to  produce  the  clock- 
wise movement.  If  no  current  were  flowing  in  the 
wire  the  field  would  show  uniform  radial  lines  of 
force  everywhere  similar  to  those  in  the  left-hand 
side  of  Figure  28  and  the  wire  would  remain  at  rest. 
Again,  then,  Faraday's  conception  of  lines  of 
forces  enables  us  to  picture  the  cause  of  electrical 
action.  As  in  the  generation  of  electric  currents 
by  induction,  we  saw  that  whenever  a  wire  was 
moved  through  a  field  of  force,  or  cut  the  lines,  an 
[133] 


Electricity:   Its  History  and  Development 

e.  m.  f.  was  induced,  tending  to  cause  a  current  to 
flow  through  the  wire,  so,  in  the  production  of 
motor  action,  we  find  that  whenever  a  current  flows 
at  right  angles  to  a  field  of  force,  or  whenever  the 
lines  of  force  are  distorted  by  a  current,  a  mechan- 
ical pressure  is  produced  tending  to  move  the  con- 
ducting wire. 

Many  of  these  conceptions,  however,  developed 
gradually  in  the  fifty  years  following  Faraday's 
discovery.  At  first  the  developments  were  simply 
modifications  of  his  original  device.  A  horseshoe 
magnet  was  substituted  for  the  bar  magnet  and  ar- 
ranged as  at  A,  Figure  29 ;  and  as  the  wire  tended 
to  rotate  in  one  direction  about  the  north  pole,  and 
in  the  opposite  direction  about  the  south,  as  shown 
by  the  dotted  semicircles,  the  actual  resultant  mo- 
tion was  in  the  direction  of  the  arrow.  The  wire, 
that  is,  was  thrown  out  of  the  mercury  and  thus 
broke  the  circuit ;  then,  of  course,  the  action  ceased 
and  the  wire  fell  back,  this  cycle  being  repeated  as 
long  as  a  battery  was  connected.  In  1823,  Barlow 
substituted  the  star  wheel  shown  at  B,  Figure  29, 
in  which  a  new  point  of  the  star  entered  the  mer- 
cury just  as  the  preceding  point  was  pushed  out, 
continuous  rotation  resulting. 

And  so  on  through  forty  years  various  appli- 
cations of  the  original  principle  were  made  in  the 
attempt  to  rival  the  steam  engine  with  electro- 
[134] 


The  Electrical  Revolution 

magnetic  engines,  as  the  motors  were  universally 
called.  In  1838,  Jacob!  produced  a  motor-driven 
boat  attaining  a  speed  of  four  miles  an  hour.  A 
few  years  later  Professor  Page  of  the  Smithsonian 
Institution  originated  a  design  that  has  been  pre- 
served in  the  toy  electric  engines,  so  called,  in  which 
iron  plungers  are  alternately  pulled  into  solenoids 
arranged  on  opposite  sides  of  a  "  walking  beam  " 
similar  to  those  used  in  side  wheel  steamboats,  the 
motion  being  transmitted  through  a  crank  to  a 
heavy  flywheel.  This  Page  engine,  installed  on  an 
electric  car,  even  made  a  10-mile  trial-run  from 
Bladensburg  to  Washington  in  two  hours,  and 
would  have  done  better  if  one  of  the  battery  jars 
had  not  broken.  Throughout  the  development,  the 
limitations  of  the  primary  battery  as  a  source  of 
power  were  keenly  felt.  In  1857  the  British  Insti- 
tute of  Civil  Engineers  discussed  with  deep  interest 
the  possibility  of  producing  a  horsepower  from  less 
than  45  pounds  of  zinc  and  decided  that  until  this 
could  be  done  coal  and  the  steam  engine  were  the 
only  practicable  source  of  power. 

It  was,  therefore,  not  until  the  development  of 
engine-driven  electric  generators,  which  began 
about  1870,  that  the  commercial  use  of  motors  was 
practicable,  and  several  independent  workers  soon 
found  that  in  developing  this  generator  a  much 
better  form  of  motor  had  also  been  developed ;  for 
[135] 


Electricity:   Its  History  and  Development 

the  generator  and  motor  proved  to  be  the  same 
machine,  mechanical  power  being  supplied  in  one 
case  and  electrical  power  produced,  while  in  the 
other  electrical  power  was  supplied  and  mechanical 
power  produced. 

This  can  be  made  clear  by  considering  Figure  30. 
With  currents  flowing  as  shown,  Fleming's  left- 
hand  rule  indicates  that  the  reactions  of  both  ends 
of  the  loop  aid  in  producing  rotation  about  the 
axis.  As  soon  as  the  plane  of  the  loop  is  at  right 
angles  to  the  lines  of  force  which  pass  from  the 
north  to  the  south  pole  the  tendency  to  rotate  stops, 
for  the  push  in  opposite  directions  on  the  two  wires 
is  now  in  a  straight  line  and  merely  tends  to  force 
the  sides  of  the  loop  farther  apart.  If  there  is 
now  sufficient  momentum  to  carry  the  loop  slightly 
beyond  this  position,  called  a  dead  center,  the  com- 
mutator reverses  the  direction  of  current  flow 
through  the  loop,  the  push  changes  from  an  out- 
ward to  an  inward  direction,  and  another  half  revo- 
lution is  performed,  so  that  by  adding  a  flywheel  a 
fairly  uniform  speed  of  rotation  may  be  obtained. 

Now  suppose  a  second  loop  exactly  similar  to 
this  is  attached  to  the  same  axle  at  right  angles  to 
the  first  and  connected  to  a  separate  commutator 
with  brushes  arranged  in  series  with  the  first  pair. 
Evidently,  when  the  first  loop  is  on  a  dead  center 
the  second  is  in  a  position  where  the  push  exerts 
[136] 


Fig.  30.     Further  development  of  Faraday's  device 
showing   evolution   of  modern   motor   armature 


Six  pole  modern  motor  showing  multi  bar  commutator  at 
(c),  brushes  at   (b).     Armature  conductors  or 
winding  at  (w)   and  at   (f)   field  coils  re- 
placing permanent  magnet  of  Fig.  30 

{.Page  137 


The  Electrical  Revolution 

the  maximum  tendency  to  rotation,  or,  in  other 
words,  the  position  of  maximum  torque,  and  with 
this  arrangement  the  flywheel  can  be  eliminated. 
By  placing  more  and  more  loops  at  intermediate 
angles  the  turning  tendency  or  torque  can  be  made 
more  and  more  uniform  and  stronger  and  stronger 
for  all  positions  of  the  loops,  and  by  placing  an 
iron  core  within  this  hollow  cylinder  of  loops  the 
number  of  lines  of  force  passing  from  the  north  to 
the  south  pole  will  be  greatly  increased.  Careful 
experiments  have  shown  that  the  push  on  a  wire  is 
equal  to  the  strength  of  the  current  flowing  multi- 
plied by  the  strength  of  the  field,  so  that  the  iron 
core  again  greatly  increases  the  torque.  But  all 
these  separate  loops  with  separate  commutators 
would  make  a  very  cumbrous  machine  and  it  was 
not  until  Siemens,  Gramme,  Edison,  and  a  score  of 
other  pioneers  developed  schemes  whereby  these 
loops  could  be  arranged  in  a  continuous  winding  on 
the  iron  core  (the  winding  having  short  connecting 
taps  from  properly  spaced  points  to  a  single  com- 
mutator with  many  bars)  that  the  modern  armature 
was  realized.  Returning  to  the  simple  loop  of  Fig- 
ure BO,  we  see  that  as  it  rotates  as  a  motor  armature 
the  conductors  cut  lines  of  force,  and  applying 
Fleming's  right-hand  rule  (see  Chapter  V)  we  find 
that  an  e.  m.  f.  is  generated,  tending  to  cause  a 
current  to  flow  in  the  direction  opposite  to  the 
[137] 


Electricity:   Its  History  and  Development 

motor  current.  If,  then,  we  placed  a  pulley  on 
the  shaft  and  turned  the  loop  mechanically  it  would 
generate  currents ;  or,  a  motor  is  simply  the  reverse 
of  a  generator. 

The  e.  m.  f.  generated  in  the  motor  armature  by 
its  motion  —  the  counter  e.  m.  f.,  or  back  e.  m.  f., 
as  it  is  called  (because  it  acts  against  the  e.  m.  f. 
which  is  causing  the  rotation),  has  a  very  impor- 
tant bearing  on  the  motor  action.  If  an  armature 
at  rest  is  connected  to  a  constant  e.  m.  f.,  the  cur- 
rent flowing  through  it  is,  in  accordance  with 
Ohm's  law,  equal  to  the  applied  e.  m.  f.  divided  by 
the  armature  resistance.  But  as  the  motor  speeds 
up,  the  counter  e.  m.  f.  is  generated  and  becomes 
greater  and  greater,  thereby  reducing  the  current 
through  the  armature  more  and  more,  until  a  speed 
is  reached  such  that  the  impressed  e.  m.  f .  minus  the 
counter  e.  m.  f .  forces  a  current  through  the  arma- 
ture resistance  just  sufficient  to  give  the  magnetic 
push  required  for  turning  the  armature  at  that 
speed.  If  a  load  is  put  on  the  motor,  the  armature 
slows  down  and  the  counter  e.  m.  f .  decreases  suf- 
ficiently to  allow  the  current  to  increase  to  the 
amount  required  for  the  stronger  push.  By 
making  the  armature  resistance  very  low  a  slight 
decrease  in  speed  may  give  a  large  increase  in  cur- 
rent, so  that  the  motor  can  be  made  to  have  nearly 
the  same  speed  from  no  load  to  full  load,  or  good 
[138] 


The  Electrical  Revolution 

speed  regulation.  In  this  case,  however,  the  cur- 
rent before  the  motor  starts  will  be  great  enough 
to  burn  the  commutator  seriously,  so  it  is  necessary 
to  use  a  variable  resistance  in  series  with  the  arma- 
ture to  limit  the  current  until  the  armature  speeds 
up,  when  this  starting  resistance  is  gradually  re- 
moved or  cut  out. 

Early  in  the  development  of  motors  and  gen- 
erators the  permanent  field  magnets  were  replaced 
with  electro-magnets  giving  stronger  and  readily 
controlled  magnetic  fields.  In  scries  machines  the 
current  passes  through  the  field  winding  and  thence 
through  the  armature,  and  in  consequence  a  series 
motor  can  exert  a  very  heavy  pull  at  starting,  as 
the  rush  of  current  through  the  armature  at  rest 
gives  a  very  strong  field.  Series  motors  are,  there- 
fore, used  for  electric  cars  and  similar  service.  In 
shunt  machines,  on  the  other  hand,  the  field  is  con- 
nected in  parallel  with  the  armature,  and  its 
strength  depends  only  upon  the  impressed  e.  m.  f. 
Shunt  motors,  therefore,  exert  lower  starting 
torque  but  have  very  constant  speed  regulation. 
Combinations  of  the  two  methods  of  field  connec- 
tions are  also  made ;  and  in  alternating  current  mo- 
tors further  phenomena  are  encountered,  giving  a 
wide  range  of  characteristics  adaptable  to  almost 
every  class  of  service. 

This  wonderful  adaptability  of  the  motor,  its 
[139] 


Electricity:   Its  History  and  Development 

remarkable  speed  control,  its  cleanliness,  reliability, 
and  efficiency,  the  range  of  sizes  in  which  it  can 
be  made  from  the  tiny  fan  and  sewing  machine 
motors  to  the  6600  H.  P.  giants  used  in  the  steel 
mills,  and  the  ease  with  which  power  can  be  trans- 
mitted to  it  from  great  distances,  have  gone  far 
to  reverse  the  relation  between  steam  and  electric- 
ity, so  much  deplored  by  the  scientists  of  '57,  and 
so  have  given  to  Faraday's  "  electro-magnetic  rota- 
tions "  or  "  electrical  revolutions "  a  fundamental 
share  in  the  marvelous  industrial  advance  of  the 
last  thirty  years,  which  in  quite  a  different  sense 
and  with  even  larger  truth  is  generally  accredited 
to  The  Electrical  Revolution. 


[140] 


XIII 
A  BLACKSMITH  AND  HIS  DREAM 

SOMETIME  about  1834,  Thomas  Davenport  of 
Brandon,  Vermont,  wearied  of  the  routine  of 
horseshoeing  and  wagon  repairs  which  his  reputa- 
tion of  "  good  blacksmith  "  brought  him,  and  saw 
visions  of  a  new  form  of  transportation  which 
should  make  horseshoeing  forever  unnecessary.  The 
news  of  Faraday's  discovery  of  electrical  rotation 
and  descriptions  of  crude  forms  of  motors  were  just 
beginning  to  attract  general  attention,  and  to 
Davenport  came  the  idea  of  applying  the  motor  to 
the  propulsion  of  a  vehicle  or  car.  By  1835  he 
had  developed  a  working  model  running  on  a  cir- 
cular track  a  few  feet  in  circumference,  and  held  a 
public  exhibition  in  Springfield,  Massachusetts,  and 
later  in  Boston. 

He  became  so  interested,  indeed,  in  the  possibili- 
ties of  electric  motors  that  he  designed  over  a  hun- 
dred operative  forms  during  the  next  six  years, 
applied  them  to  printing  presses  and  other  ma- 
chines, and  finally  secured  from  the  Patent  Office  a 
grant  of  a  claim  for  "Applying  magnetic  and 
[141] 


Electricity:  Its  History  and  Development 

electro-magnetic  power  as  a  moving  principle 
for  machinery,  or  in  any  substantially  the  same 
principle." 

Apparently  he  was  completely  equipped  as  the 
successful  pioneer  in  electric  traction,  but  —  he  was 
just  fifty  years  ahead  of  his  neighbors.  To  them 
his  railway  was  only  an  interesting  toy,  and  the 
circular  track  and  the  first  electric  car  were,  like 
their  inventor,  forgotten.  Some  sixty  years  later, 
after  the  electric  railway  had  been  successfully  de- 
veloped by  other  men,  the  model  was  found  and  the 
details  of  Davenport's  career  unearthed  —  but  the 
fundamental  patent  had  long  expired. 

It  is  noteworthy  that  in  Davenport's  railway  the 
rails  were  used  to  conduct  current  to  the  motor,  one 
rail  being  positive  and  the  other  negative;  the 
wheels  on  one  side  of  the  car  were  insulated  from 
those  on  the  opposite  side  and  the  motor  was  con- 
nected to  wires  making  contact  with  these  wheels. 
Other  early  railways  were  almost  all  based  on  the 
attempt  to  carry  a  primary  battery  in  the  car.  The 
first  of  these  self-contained  electric  locomotives  was 
made  by  a  Scotchman,  Robert  Davidson,  in  1838, 
and  in  a  trial  run  on  the  Edinburgh  and  Glasgow 
Railway  attained  a  speed  of  four  miles  an  hour. 
Then  came  Professor  Page's  1851  car,  which  we 
noticed  in  the  last  chapter,  and  several  other  similar 
cars,  all  doomed  to  failure  through  dependence  on 
[142] 


A  Blacksmith  and  His  Dream 

the  expensive  and  unreliable  production  of  energy 
by  the  battery. 

But  the  idea  of  transmitting  the  electric  power 
from  a  central  stationary  point  to  the  moving  car, 
as  at  first  contemplated  by  Davenport,  was  gaining 
adherents.  The  use  of  the  rails  as  conductors  was 
patented  in  England  in  1840;  in  1855  an  English 
patent  was  issued  for  the  use  of  an  overhead  con- 
ductor, the  trolley  wire  of  today;  and  then  for 
twenty  years  all  progress  ceased  —  the  electric  bat- 
tery could  not  compete  with  steam.  No  sooner, 
however,  was  the  steam-driven  electric  generator 
developed  than  the  possibilities  of  the'  lighter  equip- 
ment, more  frequent  stops,  and  smokeless  operation 
of  electric  cars  began  again  to  attract  pioneers  in 
all  parts  of  the  world. 

In  1875,  a  poor  mechanic,  George  F.  Green, 
built  a  model  railway  at  Kalamazoo,  Michigan, 
which  he  operated  by  a  battery ;  but  he  abandoned 
it  when  he  found  that  he  could  not  construct  the 
dynamo  he  realized  was  necessary  for  commercial 
success.  In  1879,  at  the  Berlin  Exposition,  the 
firm  of  Siemens  &  Halske  constructed  a  road  one- 
fourth  mile  in  length  on  which  a  small  locomotive 
drew  three  cars,  carrying  about  twenty  people. 
The  power  was  transmitted  from  a  Siemens  dynamo 
through  a  single  insulated  rail  laid  between  the 
track  rails  to  another  similar  dynamo  mounted  on 
[143] 


Electricity:   Its  History  and  Development 

the  locomotive  to  serve  as  a  motor,  thus  early 
exemplifying  the  present  third  rail  system. 

Simultaneously  in  this  country,  fundamental  ad- 
vances were  made  by  Stephen  D.  Field  and  Edison. 
Indeed,  in  the  words  of  Frank  J.  Sprague,  himself 
one  of  the  greatest  pioneers  in  the  electric  railway 
field,  "  Edison  was  perhaps  nearer  than  any  other 
on  the  verge  of  great  possibilities,  had  it  not  been 
that  he  was  intensely  absorbed  in  the  development 
of  the  electric  light."  As  a  part  of  his  work  on 
the  light  and  its  applications,  Edison  had  succeeded 
in  so  improving  the  d}^namo  as  to  raise  the  efficiency 
of  converting  mechanical  to  electrical  power  from 
about  40%  to  nearly  90% ;  and  although  his 
claims  were  declared  absurd  by  most  electrical  men, 
who  asserted  that  50%  could  be  shown  mathe- 
matically to  be  the  highest  possible  efficiency,  he  had 
such  faith  in  these  claims  that  he  took  time  in  the 
midst  of  his  work  in  electric  lighting  in  the  spring 
of  1880  to  superintend  the  building  of  an  experi- 
mental road  about  one-third  of  a  mile  long,  near 
his  laboratory  at  Menlo  Park.  On  this  road  he 
hoped  to  demonstrate  the  results  attainable  with 
dynamos  of  90%  efficiency,  used  both  as  generators 
and  motors.  And  he  did. 

As  can  be  seen  from  Figure  31,  a  locomotive  was 
used  to  draw  three  cars  on  a  track  of  light  rails  laid 
more  or  less  haphazard  without  ballast.  At  one 
[144] 


00 


B 

§ 
E 

I 
I. 


n> 

I 


Fig.  32.  Original 
Edison  dynamo 
used  either  as  gen- 
erator or  motor 


Modern  G.  E.  "Split-frame"  40  h.  p.  railway  motor  used 

in  both  2  and  4-motor  equipments,  giving  each 

car  a  maximum  of  80-160  h.   p. 


A  Blacksmith  and  His  Dream 

point  of  the  road  a  drop  of  60  feet  occurred  in 
a  distance  of  300  feet,  and  the  curves  were  of 
startlingly  short  radius,  but  after  a  year  of  work, 
speeds  of  40  miles  an  hour  were  obtained.  The 
locomotive  consisted  simply  of  one  of  Edison's 
regular  12  H.  P.  generators  (Figure  32)  mounted 
on  its  side  on  the  platform  and  connected  to  the 
axle  of  the  truck  through  friction  gears,  later  re- 
placed by  belts  and  pulleys.  The  wheels  were  in- 
sulated from  the  axle  and  the  rails  used  to  form  the 
electric  circuit,  just  as  in  Davenport's  model,  the 
rails  being  insulated  from  each  other  by  inter- 
posing tar  canvas-paper  between  them  and  the  ties. 
At  first  the  motor  was  connected  directly  to  the 
circuit  to  start,  but  this  was  found  to  jolt  the 
apparatus  so  severely  that  resistance  boxes,  or 
frames  carrying  coils  of  high  resistance  wire,  were 
introduced  into  the  circuit  to  reduce  the  starting 
current,  and  were  then  gradually  short-circuited 
and  so  removed  as  the  motor  speeded  up  and  its 
counter  e.  m.  f.  became  sufficient  to  limit  the  cur- 
rent to  the  normal  value.  Many  accidents  occurred 
on  the  flimsy  track,  and  much  equipment  was 
demolished.  But  commercial  electric  locomotive 
operation  was  well  in  sight  when  Edison's  patent 
applications  were  declared  in  interference  with 
those  of  Stephen  Field  and  after  long  negotiations 
the  patents  of  both  were  bought  by  "  The  Electric 
[145] 


Electricity:   Its  History  and  Development 

Railway  Company  of  America  "  ;  the  work  of  devel- 
opment was  assigned  to  Field,  and  Edison  turned 
his  attention  to  other  matters. 

The  Electric  Railway  Company  exhibited  an 
electric  locomotive  named  "  The  Judge,"  in  Chicago 
in  1883,  which  hauled  nearly  25,000  persons  in  an 
attached  passenger  car  during  the  two  and  a  half 
weeks  of  the  Chicago  Railway  Exposition.  "  The 
Judge"  did  good  service  also  in  awakening  public 
interest  at  other  expositions,  but  aside  from  this  the 
work  of  Edison  and  Field  hardly  exercised  the  in- 
fluence which  it  deserved. 

Indeed,  the  first  commercial  railway  had  already 
been  installed  at  Lichterfeld,  Germany,  in  1881 ; 
but  the  real  beginning  of  the  modern  development 
is  generally  credited  to  the  United  States  and  to 
Sprague  in  recognition  of  his  work  in  building  the 
system  at  Richmond,  Virginia.  For  in  place  of 
the  one-  or  two-car  roads  previously  operated,  the 
Richmond  contract,  started  in  the  spring  of  1887, 
included  "the  building  of  a  generating  station, 
erection  of  overhead  lines,  and  the  equipment  of 
fort}7  cars,  each  with  two  7%  H.  P.  motors  on  plans 
largely  new  and  untried."  In  this  system  the 
e.  m.  f .  employed  was  raised  to  450  volts,  the  trol- 
ley wire  being  maintained  at  this  pressure  above 
the  track  rails,  which  were  used  as  the  return 
circuit. 

[146] 


G.  E.  type  k-36-f  controller,  showing  drum  and  contact 

fingers  for  accelerating  car  from  standstill  to 

maximum    speed,    using    "series    parallel" 

system   of   control  [Page  149 


A  Blacksmith  and  His  Dream 

The  importance  of  this  increase  in  pressure  is 
easily  seen.  It  will  be  remembered  that  we  found, 
in  considering  the  heat  generated  by  the  electric 
current,  that  any  current  in  flowing  through  a  re- 
sistance wastes  energy  as  heat  at  a  rate  equal  to  the 
square -of  the  current  in  amperes  multiplied  by  the 
resistance  in  ohms.  We  also  found  that  the  rate 
of  electric  energy  supply  is  measured  by  the 
product  of  the  current  and  the  pressure  at  which  it 
is  supplied.  Thus  a  10  H.  P.  motor  uses  energy 
at  the  rate  of  7,460  watts ;  and  this  rate  at  74.6 
volts  means  a  current  of  100  amperes;  while  at  746 
volts  only  10  amperes  will  be  required.  If  now  the 
current  must  flow  through  a  circuit  having  1  ohm 
resistance,  100x100x1  or  10,000  watts  will  be  lost 
as  heat  if  power  is  delivered  at  74.6  volts,  while 
only  10x10x1  or  100  watts  will  be  lost  if  power  is 
delivered  at  746  volts.  That  is,  the  transmission 
loss  decreases  as  the  square  of  the  increase  in  volt- 
age; and  by  raising  the  trolley  pressure  from  100 
volts  to  450  volts,  and  later  to  600  volts  —  the 
present  standard  —  Sprague  decreased  the  trans- 
mission loss  to  5%  and  then  to  3%  of  its  amount 
in  the  early  100- volt  railways. 

But  the  loss  was  still  too  high  and  the  only 
safe  means  to  get  further  reduction  was  to  lessen 
the  resistance  of  the  circuit  by  using  larger  con- 
ductors. As  the  size  of  trolley  wire  which  can  be 
[147] 


Electricity:   Its  History  and  Development 

conveniently  suspended  by  brackets  or  span  wires 
was  comparatively  small,  Sprague  adopted  a  sys- 
tem of  large  feeders  carried  on  the  poles  or  under- 
ground, and  cross  connected  to  the  trolley  wire  at 
frequent  intervals.  This  made  the  trolley  prac- 
tically one  strand  of  the  large  feeder  cable  and  the 
resistance  of  the  trolley  circuit  could  easily  be  re- 
duced. In  spite  of  the  great  gain  from  using 
feeders,  however,  the  loss  was  still  too  large,  for 
the  resistance  of  the  trolley  was,  of  course,  only  a 
part  of  that  of  the  entire  circuit.  The  rail  return 
was  found  to  have  such  a  high  resistance  at  certain 
joints  that  the  return  current  left  the  track  and 
flowed  along  parallel  water  and  gas  pipes,  leading 
not  only  to  high  transmission  losses  but  to  elec- 
trolysis, gradually  destroying  the  pipes  and  rails 
just  as  it  gradually  consumes  the  electrode  of  an 
electro-plating  cell. 

Efforts  were  at  once  begun  to  lower  the  resist- 
ance of  the  track  by  connecting  the  successive  rails 
by  heavy  copper  wires  at  each  j  oint  and  these  wires 
or  bonds  have  gradually  been  increased  in  size  and 
perfected  in  connection,  until  today  the  bonded 
joints  have  lower  resistance  than  an  equal  length 
of  rail.  In  the  best  construction,  indeed,  the  ques- 
tion of  bonds  is  so  important  and  so  expensive 
that  it  is  found  cheaper  to  weld  the  rail  into  one 
continuous  length  with  electrically  generated  heat 
[148] 


A  Blacksmith  and  His  Dream 

and  to  reduce  its  resistance  further  by  running 
heavy  copper  ground  return  cables  or  negative 
feeders  connected  to  the  rail  at  convenient  points. 

The  method  of  starting  and  controlling  the  mo- 
tors in  the  Richmond  cars  also  contained  great  im- 
provements; for  although  the  principles  of  the 
"  series-parallel "  control  had  been  outlined  by  Dr. 
Hopkinson  in  1881,  Sprague  worked  out  the  prac- 
tical problems.  With  this  system  the  armatures  of 
the  two  motors  are  connected  at  starting  in  series 
with  one  another  and  with  a  resistance  which  is  re- 
duced by  steps  as  the  car  speeds  up  until  the  motors 
are  in  series  directly  across  the  full  line  pres- 
sure, each  thus  receiving  one-half  of  this  pressure 
and  so  giving  the  car  about  half  its  maximum  speed. 
Each  motor  is  next  connected  to  the  line  separately 
in  series  with  a  resistance,  and  the  two  resistances 
are  reduced  together  step  by  step  until  each  motor 
receives  the  line  pressure,  the  two  motors  thus 
being  in  parallel,  and  the  maximum  speed  is  ob- 
tained. These  complicated  changes  are  made  by  a 
switching  arrangement  called  a  controller,  in  which 
a  drum  carrying  several  connecting  segments,  and 
rotated  by  the  motorman  through  a  crank  handle, 
completes  the  circuit  as  desired  between  various 
spring  contacts. 

The  motors  in  the  Richmond  system,  too,  were 
carried  on  the  trucks  and  geared  to  the  axles  as  in 
[149] 


Electricity:   Its  History  and  Development 

m 

the  latest  cars,  and  although  many  minor  improve- 
ments were  required  the  essentials  were  well  in  hand. 

The  development  since  1887  is  almost  inconceiv- 
able. At  the  beginning  of  that  year  there  were 
less  than  forty  miles  of  electric  railways  and  not 
more  than  forty  cars  in  the  United  States.  Ten 
years  later  about  20,000  miles  of  track  were 
equipped,  and  50,000  cars  were  in  service,  repre- 
senting an  investment  of  one  and  a  half  million 
dollars ;  and  today  the  industry  is  capitalized  at 
over  $4,000,000,000. 

But  to  his  neighbors  Davenport  seemed  always  a 
dreamer. 


[150] 


XIV 
THE  MYSTERY  OF  THE  IRON  BOX 

VERY  early  in  the  commercial  development  of 
electric  lighting,  following  Edison's  success- 
ful manufacture  of  the  bamboo  incandescent  lamp, 
the  limitations  of  a  110-volt  transmission  pressure 
began  to  be  felt.  As  we  have  seen  in  considering 
the  electric  railway,  the  loss  of  power  as  heat  in 
the  line  conductors  increases  as  the  square  of  the 
current,  and  any  considerable  power  at  110-volt 
pressure  means  a  current  so  large  that  it  can  be 
transmitted  economically  for  only  very  short  dis- 
tances. The  current  corresponding  to  a  given 
power  can  be  decreased  to  any  desired  extent,  of 
course,  by  proportionately  increasing  the  line  pres- 
sure, as  power  is  equal  to  the  product  of  volts  and 
amperes,  but  in  the  case  of  the  incandescent  lamp 
the  pressure  was  fixed  at  110  volts.  Efficient  fila- 
ments became  too  fragile  for  satisfactory  service 
if  made  for  high  pressures,  and  thus  the  problem 
was  reduced  at  once  to  finding  some  way  of  trans- 
mitting power  to  the  consumer  at  a  fairly  high  volt- 
age and  then  changing  this  pressure  to  110  volts 
before  it  was  applied  to  the  lamps. 
[151] 


Electricity:   Its  History  and  Development 

One  method  available  was  evidently  to  generate 
D.  C.  current  at,  say,  550  volts  and  transmit  at 
this  pressure  to  the  user's  premises,  where  a  550- 
volt  motor  should  be  installed  to  drive  a  110-volt 
generator.  But  rotating  machines  were  expensive 
and  required  constant  attention,  and  hence  this 
scheme  was  feasible  for  large  consumers  only.  Very 
soon,  too,  demand  for  power  began  to  arise  at  such 
considerable  distances  from  the  central  station  that 
even  550  volts  was  too  low  for  economy,  and  great 
difficulties  were  experienced  in  building  D.  C.  ma- 
chines which  would  successfully  generate  higher 
pressures.  The  direct  current  commutator  espe- 
cially became  a  well-nigh  insurmountable  obstacle 
when  the  pressure  between  adjacent  segments  was 
raised  above  a  few  volts,  and,  although  a  number 
of  systems  were  built  and  operated  by  using  sev- 
eral D.  C.  generators  connected  in  series  —  notably 
one  at  Brescia,  transmitting  700  horsepower  twelve 
miles  at  15,000  volts  —  the  plan  was  much  too  com- 
plicated and  costly  for  American  urban  practice. 
In  the  meantime,  however,  alternating  currents  were 
beginning  to  be  investigated  and,  through  the 
work  of  William  Stanley  in  1885,  at  Great  Bar- 
rington,  Mass.,  soon  came  to  dominate  the  field 
wherever  transmission  to  a  considerable  distance 
was  required. 

To  understand  Stanley's  work  it  is  necessary  to 
[152] 


The  Mystery  of  the  Iron  Box 

review  the  action  of  an  alternating  current  gen- 
erator of  the  simple  form  shown  in  Figure  33.  If  the 
conducting  loop  represented  by  the  heavy  line  is 
rotated  in  a  clockwise  direction,  current  will  flow 
during  the  first  half-revolution  (see  Fleming's 
right-hand  rule,  page  63)  from  the  inner  to  the 
outer  collecting  ring  through  the  loop  and  thence 
from  the  outer  ring  through  the  external  circuit 
and  then  back  to  the  inner  ring.  During  the  sec- 
ond half-revolution  the  flow  will  be  from  the  inner 
to  the  outer  ring  through  the  external  circuit,  and 
so  on,  reversing  in  direction  every  half -revolution. 
At  any  particular  instant  the  strength  of  the  cur- 
rent in  a  straight  connecting  conductor  is  propor- 
tional to  the  generated  e.  m.  f.,  in  accordance  with 
Ohm's  law,  and  this  e.  m.  f .  is  in  turn  proportional, 
as  we  know,  to  the  rate  at  which  lines  of  force 
cut  or  are  cut  by  the  conductor.  Thus  at  the  in- 
stant shown  by  the  heavy  line  drawing  of  the  loop, 
the  two  sides  are  moving  practically  parallel  to 
the  lines  of  force,  so  that  no  cutting  occurs,  and 
hence  no  e.  m.  f.  is  generated;  while  as  uniform 
rotation  continues  the  conductor  cuts  more  and 
more  lines  for  each  degree  added  to  the  angle  of 
motion  until  it  reaches  the  position  shown  by  the 
dotted  loop,  where  the  rate  of  cutting  and  there- 
fore the  induced  e.  m.  f.  is  at  a  maximum.  Con- 
tinuing the  rotation  the  e.  m.  f.  decreases  until  at 
[153] 


Electricity:   Its  History  and  Development 

the  end  of  a  half -revolution  from  the  initial  posi- 
tion it  is  again  zero,  whence  it  continues  to  de- 
crease or  (what  is  really  the  same  thing)  begins 
to  increase  to  a  maximum  again  in  the  opposite 
direction. 

The  successive  changes  in  the  value  of  the 
e.  m.  f.  are  best  shown  by  a  curve  similar  to  that 
in  Figure  34,  where  the  passage  of  time  is  repre- 
sented by  increasing  distance  from  the  vertical  line 
at  the  left  along  the  central  horizontal  line  or  axis, 
and  the  magnitude  of  the  induced  e.  m.  f.  at  any 
instant  by  the  height  of  the  curve  above  or  below 
this  axis.  Figure  34  thus  indicates  a  pressure  in- 
creasing from  0  volts  to  a  positive  maximum,  and 
decreasing  to  zero  in  1/50  of  a  second,  then  de- 
creasing further  to  a  negative  maximum,  and  so 
back  to  0,  having  passed  through  the  complete 
sequence  or  cycle  of  values  in  1/25  of  a  second. 
Twenty-five  cycles  of  pressure  per  second  will  thus 
be  produced  as  long  as  the  generator  continues  to 
revolve  at  normal  speed,  or,  as  it  is  generally 
stated,  the  frequency  is  25  cycles.  The  figure  is 
reproduced  from  a  photographic  record  of  the  in- 
stantaneous cyclic  variation  in  the  pressure  of  the 
Commonwealth  Edison  Co.'s  25-Cycle  System,  the 
complete  curve  from  the  vertical  line  to  the  point 
marked  2/50  being  frequently  called  the  wave 
form  of  the  system  —  a  term  which  has  no  rela- 
[154] 


Fig.  33.     Simple  alternating  current  generator 

[Page  153 


Fig.  34.     Alternating  pressure  wave  form  of  Common- 
wealth   Edison    Company's    25-cycle    system 


Fig.  35.     (a)  Simple  transformer  developed  from  Fara- 
day's anchor  ring 
(b)    Induction  coil  type  of  transformer 

[Page  156 


Fig.  36.     Elementary  A.  C.  circuit  showing  two  trans- 
formers connected  in  parallel  to  high  tension 
line  and  supplying  customers  with 

9  and  5  lamps  respectively  [Page  151 


The  Mystery  of  the  Iron  Box 

tion,  however,  to  the  electric  waves  used  in  wrireless 
telegraphy. 

Such  an  alternating  pressure  applied  to  the  ter- 
minals of  an  incandescent  lamp  produces  a  current 
varying  just  as  the  voltage  varies,  or  having  just 
the  same  wave  form,  and  it  has  been  found  that 
heat  is  produced  thereby  at  the  same  rate  as  by 
a  direct  curent  0.7  as  great  as  the  maximum  value 
of  the  alternating  current.  The  effective  value  of 
an  alternating  current  is  thus  said  to  be  0.7  of 
its  maximum  value.  This  relation  varies  with  the 
wave  form,  and  in  some  circuits  the  current  wave 
form  is  very  different  from  the  wave  form  of  the 
pressure  causing  it  to  flow ;  indeed  alternating  cur- 
rents introduce  many  questions  too  complex  for  the 
present  discussion.  But  it  should  be  fairly  clear 
from  the  above  that  any  given  alternating  current 
has  a  continuously  changing  instantaneous  value, 
and  that  the  effect  of  the  recurring  series  of  instan- 
taneous values  in  producing  heat  or  doing  other 
work  is  exactly  equivalent  to  some  direct  current 
value  which  can  be  calculated. 

In  our  consideration  of  Faraday's  discovery  of 
the  induced  currents  in  his  anchor  ring  (see  Chap- 
ter V)  we  found  that  the  only  condition  which  must 
be  fulfilled  in  order  that  induced  currents  should 
be  produced  in  one  of  the  coils  of  wire  wound  on 
the  ring  (as  for  example,  the  right-hand  coil  of  A, 
[155] 


Electricity:   Its  History  and  Development 

Figure  35  )  was,  that  the  value  of  the  current  should 
be  changing  in  the  other  coil  —  in  the  left-hand 
winding  of  A.  Using  direct  currents  this  occurs 
only  when  the  circuit  through  the  left-hand  coil 
is  made  or  broken,  for  then  the  lines  of  force 
threading  the  second  coil  increase  or  decrease  and 
so  induce  e.  m.  f.'s  by  cutting  the  turns  of  the 
winding. 

Suppose  now,  however,  we  cause  an  alternating 
current  to  flow  through  the  exciting  or  primary 
coil.  As  the  current  value  changes  continuously, 
the  magnetism  —  the  number  of  lines  of  force  —  in 
the  iron  ring  or  core  will  also  change,  passing 
through  a  regular  cycle  of  values,  and  now  an 
alternating  e.  m.  f .  will  be  induced  continuously  in 
the  second  coil  or  secondary  winding.  But  the 
value  of  the  e.  m.  f .  induced,  as  in  all  other  cases, 
depends  entirely  on  the  number  of  lines  of  force 
cut  per  second,  and  since  10  lines  cutting  one  turn 
generates  the  same  e.  m.  f.  as  one  line  cutting  10 
turns,  we  can  get  any  pressure  desired  by  altering 
the  number  of  times  the  secondary  is  wound  round 
the  core,  or  the  number  of  secondary  turns.  Thus 
if  we  require  a  pressure  of  100  volts  and  we  find 
that  with  a  given  primary  and  core  a  secondary  of 
10  turns  gives  a  pressure  of  one  volt,  the  winding 
must  evidently  be  increased  100  times  or  to  1,000 
secondary  turns. 

[156] 


The  Mystery  of  the  Iron  Box 

Here  then  is  the  solution  of  the  transmission 
problem.  The  first  attempt  to  apply  it  commer- 
cially was  made  in  England  in  1883  by  Gaulard 
and  Gibbs,  using  a  modified  form  of  induction  coil 
similar  to  B,  Figure  35,  and  the  attempt  was  suffi- 
ciently promising  to  excite  interest.  But  the  real 
solution  was  reserved  for  Stanley,  who  first  con- 
ceived the  idea  of  the  alternating  circuit  shown  in 
Figure  36,  prototype  of  all  present-day  alternating 
current  or  A.  C.  transmissions. 

Working  in  an  abandoned  rubber-mill  in  1885, 
he  built  about  a  dozen  transformers,  or,  as  he  then 
called  them,  "  converters,"  to  reduce  the  primary 
pressure  of  500  volts  to  100-volt  secondary  pres- 
sure —  each  transformer  of  sufficient  current  capac- 
ity to  supply  twenty -five  16-candlepower  lamps, 
and  installed  his  system  in  one  or  two  stores  and  the 
hotel  at  Great  Barrington.  The  primary  coil  con- 
nected directly  across  500  volts  had  a  resistance  of 
only  one  ohm,  and  electricians  familiar  with  Ohm's 
law  and  with  direct  current  circuits  expected  some 
500  amperes  to  flow  through  each  primary,  burning 
up  the  transformers  and  wrecking  the  generator. 
Nothing  of  the  kind  happened  and  the  foreboders 
were  quite  ready  to  abandon  all  theories  forever 
when  they  found  that  with  the  lamps  turned  off,  or, 
in  other  words,  when  the  secondary  was  on  open 
circuit,  the  actual  current  flow  was  less  than  two  am- 
[157] 


Electricity:   Its  History  and  Development 

peres,  while  as  lamp  by  lamp  was  switched  on  in 
the  secondary  circuit  the  primary  current  increased 
proportionately,  one  ampere  in  the  secondary  cor- 
responding to  1/5  ampere  in  the  primary.  Where 
was  the  discrepancy  —  what  was  wrong  with  Ohm's 
law? 

The  explanation  was  soon  found  and  is  really 
very  simple.  Just  as,  in  the  case  of  a  motor,  an 
e.  m.  f .  which  opposes  the  flow  of  current  is  induced 
in  the  armature  by  motion  through  the  magnetic 
field,  so  in  the  primary  coil  the  variation  of  the 
field  strength,  equivalent  to  movement  of  the  mag- 
netic lines  past  the  coils,  induces  an  e.  m.  f.  in  the 
primary  simultaneously  with  the  induction  in  the 
secondary  winding.  In  the  primary  this  back 
e.  m.  f.  is  in  a  direction  opposed  to  the  flow  of 
current  and  of  such  a  value  that  the  difference  be- 
tween the  applied  and  the  back  e.  m.  f .  is  just  suffi- 
cient to  cause  a  current  to  flow  large  enough  to 
produce  the  magnetic  field  necessary  to  generate 
the  back  e.  m.  f .  In  other  words,  the  obstruction 
to  the  flow  of  an  alternating  current  through  a  wire 
wound  around  an  iron  core  is  much  greater  than 
to  the  flow  of  a  direct  current,  being  composed  of 
a  magnetic  reaction,  called  the  reactance  of  the  cir- 
cuit, as  well  as  of  the  resistance  of  the  conducting 
path.  As  current  is  allowed  to  flow  through  the 
secondary  winding  of  the  transformer  by  connect- 
[158] 


External    appearance    of    modern    lighting    transformer 
manufactured  by  General  Electric  Company 


The  Mystery  of  the  Iron  Box 

ing  lamp  filaments  or  other  conductors  across  the 
secondary  terminals,  the  effect  is  as  if  a  second 
magnetic  field  were  produced  of  such  magnitude 
and  direction  as  to  decrease  the  primary  back 
e.  m.  f.  sufficiently  to  allow  a  proportionate  increase 
in  the  primary  current. 

In  the  transformers  now  used  the  primary  cur- 
rent with  the  secondary  open-circuited  is  so  small, 
and  the  power  lost  in  the  transformer  in  heating 
the  windings  and  magnetizing  the  core  so  trifling, 
that  the  relation  —  primary  pressure  X  primary 
current  =  secondary  pressure  X  secondary  cur- 
rent—  is  very  closely  maintained.  Hence,  if  the 
primary  pressure  is  five  times  the  secondary  as  in 
the  original  transformers,  the  current  in  the  pri- 
mary will  be  only  1/5  that  in  the  secondary.  To- 
day the  most  usual  transmission  pressure  in  cities 
is  2,200  volts,  and  the  line  currents  are  thus  reduced 
to  1/20  of  the  value  at  110  volts,  or  the  losses  are 
only  1/400  of  those  in  the  original  Edison  Sys- 
tem. Moreover,  these  tremendous  economies  are 
obtained  with  absolute  safety,  for  Stanley's  designs 
have  been  modified  and  improved  until  the  primary 
and  secondary  windings  are  so  perfectly  insulated 
from  each  other  and  from  the  core  as  to  withstand 
five  times  the  highest  electrical  pressure  to  which 
they  are  ever  subjected. 

Everywhere  in  our  cities  are  to  be  seen  poles 

[159] 


Electricity:   Its  History  and  Development 

bearing  mysterious  iron  boxes  or  tanks,  in  which 
two  simple  coils  of  copper  wire  interlinked  with  an 
iron  core  are  immersed  in  highly  insulating  oil.  In 
stations  and  sub-stations  are  to  be  found  similar 
though  much  larger  tanks  containing  larger  units 
of  the  same  design.  No  noise,  no  motion,  no  atten- 
tion required,  a  toll  of  perhaps  2%  taken  from  the 
power  transformed  when  working  at  full  load,  but 
no  limitation  in  size  from  one  to  10,000  horse- 
power, and  no  limitation  in  safe  transmission  pres- 
sure from  1,000  to  140,000  volts  —  such  is  the 
modern  transformer,  direct  descendant  of  the  an- 
chor ring  of  Faraday,  applied  and  commercialized 
by  William  Stanley. 


[160] 


XV 

THE  SPIRIT  OF  ELECTRICITY 

IN  the  preceding  chapters  we  have  briefly  re- 
viewed some  of  the  discoveries  of  the  great  pio- 
neers of  the  past  and  have  followed  the  development 
of  electric  power  and  its  gradual  application  to 
the  production  of  motion,  heat,  and  chemical 
changes.  What  of  the  pioneers  of  the  immediate 
present  and  of  the  fast-approaching  future  ?  What 
new  electrical  service  is  to  be  found?  What  im- 
provements in  the  old  services  are  to  be  made, 
within  our  own  times? 

One  of  the  most  pressing  problems  of  the  world 
today  is  the  production  of  some  form  of  fertilizer 
to  replace  the  rapidly  diminishing  store  of  Chili 
saltpeter,  on  which  the  entire  food  supply  of  man- 
kind depends.  Each  crop  abstracts  nitrogen  from 
the  soil  in  large  proportion ;  and  unless  that  nitro- 
gen is  replaced,  the  earth  must  become  sterile  and 
barren.  Heretofore  this  nitrogen  has  been  replen- 
ished almost  entirely  from  the  deposits  of  the  natu- 
ral fertilizer,  sodium  nitrate  or  saltpeter,  which 
have  accumulated  through  the  ages  in  a  strip  of 
[161] 


Electricity:   Its  History  and  Development 

land  between  the  Andes  and  the  coast  ranges  of 
Chili.  But  this  supply  will  be  exhausted  in  fifteen 
years,  and  we  must  then  begin  to  draw  on  the  limit- 
less reservoir  of  nitrogen  in  the  atmosphere.  A 
limitless  reservoir!  Then  wherein  lies  any  prob- 
lem? Just  here.  The  nitrogen  in  the  air  is  a  free 
gas,  and  in  this  state  is  lifeless  and  without  effect 
on  other  substances ;  but  nitrogen  combined  or  fixed 
with  the  metal  sodium  and  the  gas  oxygen,  as  in 
Chili  saltpeter,  is  for  some  reason  one  of  the  most 
active  of  substances.  Nitrogen  gas  pumped  into 
the  soil  in  large  quantities  influences  growth  not 
at  all,  but  the  nitrogen  of  a  small  amount  of  Chili 
saltpeter  mixed  with  the  same  soil  will  increase  the 
crops  many  fold.  Fixed  nitrogen,  then,  we  must 
have,  and  for  many  years  chemists  have  been  striv- 
ing to  produce  it.  But  the  same  lifelessness  that 
makes  the  uncombined  gas  worthless  as  a  fertilizer 
makes  well-nigh  impossible  the  task  of  uniting  it 
with  other  substances.  It  appears  that  in  elec- 
tricity lies  the  only  means  of  solving  the  problem. 
As  long  ago  as  1790  Cavendish  found  that  a 
small  amount  of  nitrogen  was  combined  with  water 
vapor  to  form  nitric  acid  in  the  air  through  which 
an  electric  spark  had  passed,  and  later  investigators 
found  similar  traces  of  this  combination  in  the  at- 
mosphere after  a  thunder  shower.  The  application 
of  these  discoveries,  however,  was  made  only  a  few 
[162] 


The  Spirit  of  Electricity 

years  ago  by  Messrs.  Bradley  and  Lovejoy,  who 
began  experiments  at  Niagara.  They  used  an  ap- 
paratus giving  some  400,000  electric  sparks  per 
minute  in  a  cylinder  through  which  large  quanti- 
ties of  air,  with  its  80  per  cent  content  of  nitrogen, 
could  be  forced.  The  outgoing  air  contained  2 
per  cent  of  fixed  nitrogen  which  could  be  used  in 
chemical  reactions  to  produce  any  of  the  nitrogen 
compounds  desired. 

In  Norway,  where  electric  power  is  even  cheaper 
than  at  Niagara,  there  are  being  developed  methods 
in  which  the  air  is  passed  through  huge  electric 
arcs  with  flames  nearly  a  yard  in  diameter,  and,  al- 
though the  direct  production  of  fixed  nitrogen  from 
the  electric  spark  or  arc  is  by  no  means  a  finished 
process,  it  is  certainly  only  a  question  of  a  few 
years  before  this  new  activity  of  electricity  will  be 
one  of  its  greatest  services.  Meanwhile,  Dr.  Frank 
of  Charlottenburg  has  discovered  a  means  of  caus- 
ing calcium  carbide,  familiar  as  the  source  of 
acetylene  gas,  to  combine  with  nitrogen  when  re- 
heated in  improved  forms  of  electric  furnaces,  and 
the  compound  proves  to  be  an  excellent  fertilizer. 
This  distinctly  electrical  product  will  be  used  until 
the  direct  process  is  perfected ;  and  so,  in  one  form 
or  another,  electricity  is  fast  becoming  essential  to 
the  maintenance  of  world  life. 

The  cooperation  of  electrical  and  chemical  pio- 
[163] 


Electricity:   Its  History  and  Development 

neers  will  also  be  required  in  improving  the  effi- 
ciency of  light-production ;  and  to  understand  how 
this  is  to  be  brought  about  it  is  necessary  to  con- 
sider for  a  moment  just  what  light  is.  As  the  tem- 
perature of  a  body  is  raised,  it  begins  to  send  out 
disturbances  in  all  directions  at  perfectly  definite 
intervals,  new  disturbances  at  shorter  and  shorter 
intervals  being  given  off  as  the  body  or  radiator 
gets  hotter  and  hotter.  When  the  temperature  is 
sufficiently  high  to  cause  a  part  of  the  disturbances 
or  waves  to  occur  400  millions  of  millions  of  times 
per  second,  these  inconceivably  rapid  waves  strik- 
ing our  eyes  make  us  see  the  radiator  as  a  dull  red. 
As  faster  and  faster  waves  are  produced  the  red 
color  becomes  lighter,  changes  to  orange,  to  yel- 
low, and  finally  to  a  light  white.  But,  although 
the  temperature  is  rising,  the  slower  disturbances 
—  the  waves  which  generate  heat  when  they  strike 
any  body  —  are  still  being  sent  out  at  the  old  rate, 
and  a  large  part  of  the  work  done  on  the  body  to 
raise  its  temperature  to  incandescence  is  thus  wasted 
in  heating  the  air  or  surrounding  bodies.  Fortu- 
nately, the  higher  the  temperature  of  the  body,  the 
greater  the  percentage  of  work  which  is  turned 
into  useful  light  waves ;  and  if  we  could  get  a  lamp 
filament  at  the  temperature  of  the  sun,  about  one- 
third  of  the  electrical  work  done  on  it  would  re- 
appear as  light. 

[164] 


The  Spirit  of  Electricity 

This  means,  however,  that  the  filament  must 
withstand  a  temperature  of  5,000°  to  6,000°  Centi- 
grade (9,000°  to  10,800°  Fahrenheit),  and  car- 
bon, the  most  refractory  known  substance,  melts  at 
3,700°  C. !  Even  this  temperature  cannot  be 
reached,  except  in  the  arc  lamp,  for  as  we  found  in 
considering  the  development  of  the  incandescent 
lamp  (Chapter  XI)  carbon  begins  to  evaporate 
at  1,800°  C. ;  and  so  the  limiting  temperature 
for  filaments  today  is  just  below  the  melting 
point  of  the  metal  tungsten,  3,200°  C.  At  this 
temperature  only  one-fortieth  of  the  electrical  en- 
ergy supplied  is  converted  into  useful  light!  Is 
there  some  other  substance  with  higher  melting 
point?  and  how  shall  we  proceed  to  find  it?  All 
known  elements  fall  into  groups  according  to  their 
various  properties,  and  frequently  the  discovery  of 
a  new  element  has  rewarded  the  search  for  that 
substance  which  should  have  the  properties  required 
to  fill  a  gap  in  some  otherwise  closely  related  group. 
Such  a  gap  still  exists  among  the  metals  between 
tungsten  and  osmium  (one  of  the  first  substances 
used  for  metal  filaments),  and  the  element  to  fill 
this  gap  will  have  a  higher  melting  point  than  any 
known  substance  except  carbon.  The  search  for 
this  material  forms  a  very  real  part  of  present- 
day  pioneering;  and,  when  it  is  found,  light  pro- 
duction by  incandescent  lamps  will  probably  have 
[165] 


Electricity:   Its  History  and  Development 

reached  its  greatest  efficiency.  It  is  just  possible, 
of  course,  that  chemists  may  produce  compounds 
of  carbon  with  other  elements  which  will  have  even 
higher  melting  points ;  but  while  this  may  be  hoped, 
it  now  appears  hardly  probable. 

Are  we  then  to  accept  a  3  per  cent  yield  as  the 
maximum  attainable  in  the  generation  of  light  — 
three  watts  out  of  every  100  converted  into  the 
light  desired,  the  remaining  ninety-seven  going  to 
produce  the  invisible  and  useless  heat  waves? 
True,  this  is  a  considerably  better  result  than  can 
be  attained  in  any  of  the  older  forms  of  illuminants 
—  but  it  certainly  will  not  satisfy  the  coming  gen- 
erations whose  slogan  is  to  be  "  efficiency."  Even 
now  the  way  is  dimly  seen,  and  considerable  ad- 
vances have  been  made.  In  the  -flaming  arc  lamps 
dependence  is  no  longer  placed  on  the  incandes- 
cence of  a  solid,  but  the  carbons  used  are  first 
impregnated  with  certain  salts  of  calcium  or  other 
substances,  which  pass  into  vapor  in  the  electric  arc 
and  there  become  brilliantly  luminous,  throwing  out 
light  waves  far  in  excess  of  the  amount  corre- 
sponding to  the  temperature,  so  that  10  per  cent  or 
even  more  of  the  entire  electric  energy  is  converted 
into  light. 

This  suggests  that  electricity  in  some  way  is  di- 
rectly causing  the  disturbances  which  we  know  as 
light;  and,  further,  that  if  we  could  say  just  what 

[166] 


The  Spirit  of  Electricity 

these  disturbances  are  and  just  what  electricity  is 
efficient  light  production  could  be  easily  accom- 
plished. Here  we  are  back  to  the  question  with  which 
we  began  this  book  —  what  is  electricity?  —  and 
in  the  answer  is  to  be  found  not  only  the  solution 
of  the  problem  of  light,  but  the  way  to  appli- 
cations of  electricity  as  yet  hardly  dreamed  of. 
For  the  last  thirty  years  the  nature  of  electricity 
has  been  popularly  considered  the  greatest  of  mys- 
teries, but  even  in  1880  it  was  surely  no  more  mys- 
terious than  gravitation,  the  force  which  keeps  us 
from  flying  off  the  earth  as  water  drops  fly  from 
a  swiftly  revolving  wagon  wheel ;  no  more  unknown 
than  cohesion,  the  force  which  holds  the  particles 
of  this  paper  or  of  any  other  matter  together;  no 
more  uncanny,  indeed,  than  matter  itself.  For  is 
not  matter  so  mysterious  that  even  the  denial  of 
its  existence  forms  part  of  certain  philosophies 
and  creeds?  It  is  only  because  electricity  is  newly 
come  into  our  fields  of  knowledge,  and  so  still  has 
clinging  to  it  the  atmosphere  of  the  great  unknown, 
that  we  feel  its  mystery,  a  mystery  which  today  is 
fast  passing  as  a  conception  of  the  substance  of 
electricity  comes  almost  within  our  grasp. 

As   early   as   1873,   Clerk   Maxwell,  the   great 
Scotch  mathematical  physicist,  calculated  that  an 
electric  charge  vibrating  back  and  forth  on  a  con- 
ducting body,  or  indeed,  a  charged  body  vibrating 
[167] 


Electricity:   Its  History  and  Development 

mechanically,  would  send  out  disturbances  which 
would  travel  at  the  known  speed  of  light,  186,000 
miles  per  second.  This  could  only  mean  that 
light  waves  were  produced  by  rapidly  vibrating 
electric  charges;  and  though  the  demonstration 
was  purely  theoretical  it  so  well  accounted  for  many 
of  the  known  facts  of  light  and  electricity  that  the 
electro-magnetic  theory  of  light,  as  it  is  called, 
was  generally  accepted.  Since  that  time  Herz  and 
others  have  discovered  ways  of  producing  and  con- 
trolling vibrating  electric  charges  and  of  detecting 
and  measuring  the  speed  of  the  disturbances  sent 
out.  This  speed  has  been  found  experimentally 
to  be  that  of  light,  and  now  these  electric  waves  are 
the  almost  commonplace  means  of  transmitting  the 
signals  of  wireless  telegraphy.  The  disturbances 
which  are  easily  recognized  as  electric  waves  are 
much  slower  than  those  perceived  as  light,  occurring 
indeed  only  a  few  millions  of  times  per  second,  but 
the  identity  of  the  speed  of  transmission  goes  far 
to  verify  Maxwell's  theory.  Now,  a  vibrating 
electric  charge  is  equivalent  to  an  alternating  elec- 
tric current ;  and,  as  we  know,  any  current  is  af- 
fected by  a  magnetic  field.  If  the  theory  is  true, 
therefore,  there  should  be  some  effect  of  such  a  field 
on  the  movements  of  the  light-producing  charge. 
This  effect  was  actually  discovered  with  the  most 
refined  optical  instruments  by  Zeeman.  It  consists 
[168] 


The  Spirit  of  Electricity 

in  a  slight  change  in  the  frequency  of  vibration 
of  the  light-giving  body,  a  tiny  shift  in  the  color 
of  the  light  which  is  sent  out.  Furthermore,  from 
the  measured  amount  of  this  change  in  color,  Lar- 
mor,  Lorentz,  and  others  were  able  to  compute  the 
relation  of  the  amount  of  charge  to  the  amount  of 
matter  in  the  vibrating  body,  and  thus  to  find  that 
either  the  charge  was  comparatively  very  great  or 
the  body  of  matter  almost  infinitely  small. 

Simultaneously  another  line  of  experiment  was 
being  followed  by  Sir  William  Crookes  and  others, 
using  sealed  glass  tubes  exhausted  to  a  high  vacuum 
and  provided  with  two  electrodes  extending  through 
the  glass.  When  a  considerable  pressure  was  ap- 
plied to  the  electrodes  a  discharge  from  the  nega- 
tive electrode  took  place,  which  had  the  appearance 
of  a  column  of  luminous  gas.  This  discharge  could 
be  deflected  by  a  magnet,  would  cause  a  tiny  paddle 
wheel  to  revolve  when  properly  supported  in  its 
path,  would  cause  certain  substances  against  which 
it  struck  to  phosphoresce,  if  suddenly  stopped 
would  produce  the  Roentgen  or  X  rays,  and  in 
other  ways  behaved  like  a  stream  of  tiny  bullets, 
each  carrying  an  electric  charge.  Long  and  care- 
ful experiments  showed  this  to  be  substantially  true ; 
showed  the  discharge,  that  is,  to  be  composed  of 
flying  charged  particles,  and  these  were  found  later 
to  have  the  same  ratio  of  electric  charge  to  amount 
[169] 


Electricity:   Its  History  and  Development 

of  carrying  matter  which  had  been  computed  for 
the  Zeeman  experiments. 

Then  J.  J.  Thompson  in  Cambridge,  England, 
and  Michelson  in  Chicago  devised  experiments  of 
surpassing  delicacy  and  wonderful  accuracy,  where- 
by the  number  and  weight  of  these  particles  were 
measured,  and  at  each  step  the  conceptions  of  the 
vibrating  electric  charges  producing  light  and 
electric  radiations  became  clearer.  At  present  the 
particles  flying  at  an  inconceivable  velocity  in  the 
Crookes-tube  discharges  are  believed  to  be  disem- 
bodied unit  negative  charges,  the  "spirit"  of 
electricity.  Each  atom  of  matter  is  supposed  to 
consist  of  very  many  of  these  negative  charges, 
or  electrons,  perhaps  1,700  or  so,  combined  in  some 
way  with  corresponding  positive  charges,  and  in 
each  atom  the  charges  are  probably  rotating  in 
systems  somewhat  as  the  earth  and  planets  rotate 
about  the  sun.  The  wonderful  skill  which  has  been 
required  to  get  even  so  much  data  on  the  ultimate 
constitution  of  matter  will  be  appreciated  when  it 
is  remembered  that  in  a  single  grain  of  the  finest 
powder  there  are  something  like  a  million  million 
million  atoms,  and  these  experiments  have  dealt 
with  a  thousandth  part  of  one  of  these  incompre- 
hensibly small  particles. 

It  is  fairly  certain  now  that  an  electric  current 
in  a  wire  means  the  passing  along  of  a  series  of 
[170] 


The  Spirit  of  Electricity 

these  infinitesimal  electrons  from  atom  to  atom ;  that 
an  electric  current  in  a  liquid  means  a  constant 
procession  of  atoms  called  ions,  from  each  of  which 
a  single  negative  electron  has  been  detached  and 
the  electrical  equilibrium  thereby  destroyed;  and 
that  energy  is  transmitted  electrically  by  the  strains 
and  stresses  in  the  medium  through  which  these  elec- 
trons pass.  This  may  seem  vague,  but  our  knowl- 
edge is  still  vague  —  the  nature  of  electricity  is 
almost  known,  but  no  one  can  say  how  long  it  will 
take  to  eliminate  that  "  almost."  Many  physicists 
believe  that,  when  it  is  known,  gravitation,  cohesion, 
matter,  and  many  other  outstanding  problems  will 
be  problems  no  longer. 

Looking  back  over  the  century  and  a  half  since 
Franklin  flew  his  kite,  noting  the  splendid  achieve- 
ments of  the  devoted  pioneers,  and  realizing  the 
service  of  electricity,  it  is  but  natural  to  regard 
our  day  as  that  of  the  full-grown  manhood  of  the 
electric  age  —  but  the  real  electric  age  is  to  come ; 
the  probabilities  of  the  future  offer  far  greater 
prizes  than  the  discovery  of  a  new  continent  or 
the  settling  of  an  untilled  land ;  and  to  the  pioneers 
of  this  and  future  generations  beckons  the  spirit  of 
electricity. 


[171] 


INDEX 


INDEX 


Alternating  currents,  152  et 
seq. 

Amalgamation,  41 

Amber,  14,  20 

Ampere,  the  unit  of  current, 
70 

Ampere,  rule  for  effect  of 
current  on  magnet,  49; 
experiments  on  electrical 
attractions,  50 

Arc,  electric,  100 

Arc  lamp,  101  et  seq.;  flam- 
ing arc,  166 

Bamboo  filaments,  124 

Bell,  Alexander  Graham,  89 
et  seq. 

Calorimeter,  111 

Cascade  connection  of  Ley- 
den  jars,  30 

Cell,  the  electrical,  40 

Circuits,  closed  and  open, 
44 

Commonwealth  Edison  Co.  's 
25-cycle  system,  154 

Commutator,  66 

Compass,  14 

Conduction,  21 

Crookes,  Sir  William,  vac- 
uum tubes,  169 

" Crown  of  Cups,"  Volta's, 
40 

Current,  the  electrical,  39 

Daniels  cell,  72,  80 


Davy,  Sir  Humphrey,  100, 
109 

Earth  return,  28,  79 

Edison-Lalande  cell,  44 

Edison,  T.  A.,  94;  and  in- 
candescent  lamps,  120 

Electric  dynamo,  Edison's, 
144 

Electric  furnace,  116 

Electric  light,  98-107;  118- 
129;  163-165 

Electric  motor,  130-140 

Electric  traction,  141-150 

Electrical  machine,  20;  Far- 
aday's, 61 

Electro-magnet,  52 

Electro-magnetic  theory  of 
light,  168 

Electro-plating,  68 

Electrodes,  42 

Electrolysis,  68 

Electrolytes,  41 

Electromotive  force,  41,  45, 
72;  in  motors,  138;  in  al- 
ternating currents,  158 

Electrons,  170 

Electrophorus,  37 

Faraday's  theory  of  mag- 
netism, 53 

Franklin,  Benjamin,  26  et 
seq. 

Frog  leg,  convulsed  by  elec- 
tricity, 36 

Fuse-wire,  115 


[175] 


Index 


Galvani's  experiment,  36 

Gravity  cell,  44 

Heating  power  of  electric- 
ity, 108-117;  147 

Induced  currents,  62 

Induction  coil,  73 

Induction,  magnetic,  19 

Insulation,  22 

Ions,  171 

Joule's  law  of  relation  be- 
tween heat  and  mechan- 
ical energy,  110 

Kilowatt,  114 

Kite,  Franklin 's  experi- 
ment, 33 

Leclanche  cell,  43 

Leyden  battery,  30 

Leyden  jar,  24,  29 

Lightning,  30 

Lightning  rod,  33 

"Lines  of  force,"  53,  60, 
133 

Magnetic  field,  56 

Magnetism,  14 

Maxwell,  Clerk,  and  the 
electro-magnetic  theory 
of  light,  167 

Microphone,  93 

Morse's  telegraphic  experi- 
ments, 82 

Negative  charge,  28 

Nitrogen,  fixation  by  elec- 
.  tricity,  161 

Oersted  and  the  effect  of 
current  on  magnet,  48 

Ohm,  the  unit  of  resist- 
ance, 72 


Ohm's  law,  46,  71 

"One  fluid"  theory,  28 

Parallel  connection  of  Ley- 
den jars,  30 

Plunge  battery,  40 

Polarization,  43 

Poles,  North  and  South,  18 

Poles,  positive  and  nega- 
tive, of  cell,  45 

Positive  charge,  28 

Potential,  45 

Eeactance  of  alternating 
circuit,  158 

Rectifying  alternating  cur- 
rents, 65 

Eelay,  the  telegraphic,  84 

Eesinous  electricity,  23 

Resistance  box,  145 

Roentgen  Rays,  169 

Series  connection,  30,  40 

Solenoid,  51 

Telegraph,  77-86;  Bell's 
multiplex,  90 

Telephone,  87-97 

Thales,  14 

Transformer,  157-160 

Transmission  of  electricity, 
21;  151-160 

Tungsten  lamps,  128 

Vitreous  electricity,  23 

Volt,  the  unit  of  pressure, 
75 

Volta,  37 

Volta's  pile,  38 

Voltameter,  69 

Watt,  the  unit  of  work,  114 

"X  Rays,"  169 


[176] 


14  DAY  USE 

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LOAN  DEPT. 

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